Focus on CS8600 (not even close to done thee is a ton of these)

.editorconfig

@@ -154,6 +154,7 @@ dotnet_diagnostic.IDE2003.severity = silent
 #cleared null error types
 dotnet_diagnostic.CS8612.severity = error
 dotnet_diagnostic.CS8714.severity = error
+dotnet_diagnostic.CS8762.severity = error
 dotnet_diagnostic.CS8765.severity = error
 dotnet_diagnostic.CS8766.severity = error
 dotnet_diagnostic.CS8767.severity = error

ICSharpCode.Decompiler/CSharp/Annotations.cs

@@ -134,7 +134,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// Retrieves the <see cref="ISymbol"/> associated with this AstNode, or null if no symbol
 		/// is associated with the node.
 		/// </summary>
-		public static ISymbol GetSymbol(this AstNode node)
+		public static ISymbol? GetSymbol(this AstNode node)
 		{
 			var rr = node.Annotation<ResolveResult>();
 			if (rr is MethodGroupResolveResult)
@@ -175,7 +175,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// Retrieves the <see cref="ILVariable"/> associated with this <see cref="IdentifierExpression"/>,
 		/// or <c>null</c> if no variable is associated with this identifier.
 		/// </summary>
-		public static ILVariable GetILVariable(this IdentifierExpression expr)
+		public static ILVariable? GetILVariable(this IdentifierExpression expr)
 		{
 			if (expr.Annotation<ResolveResult>() is ILVariableResolveResult rr)
 				return rr.Variable;
@@ -187,7 +187,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// Retrieves the <see cref="ILVariable"/> associated with this <see cref="VariableInitializer"/>,
 		/// or <c>null</c> if no variable is associated with this initializer.
 		/// </summary>
-		public static ILVariable GetILVariable(this VariableInitializer vi)
+		public static ILVariable? GetILVariable(this VariableInitializer vi)
 		{
 			if (vi.Annotation<ResolveResult>() is ILVariableResolveResult rr)
 				return rr.Variable;
@@ -199,7 +199,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// Retrieves the <see cref="ILVariable"/> associated with this <see cref="ForeachStatement"/>,
 		/// or <c>null</c> if no variable is associated with this foreach statement.
 		/// </summary>
-		public static ILVariable GetILVariable(this ForeachStatement loop)
+		public static ILVariable? GetILVariable(this ForeachStatement loop)
 		{
 			if (loop.Annotation<ResolveResult>() is ILVariableResolveResult rr)
 				return rr.Variable;

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -1213,7 +1213,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// <param name="member">The node of the member which new modifier state should be determined.</param>
 		void SetNewModifier(EntityDeclaration member)
 		{
-			var entity = (IEntity)member.GetSymbol();
+			var entity = member.GetSymbol() as IEntity;
 			var lookup = new MemberLookup(entity.DeclaringTypeDefinition, entity.ParentModule);
 
 			var baseTypes = entity.DeclaringType.GetNonInterfaceBaseTypes().Where(t => entity.DeclaringType != t).ToList();
@@ -1325,7 +1325,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					foreach (var p in recordDecompiler.PrimaryConstructor.Parameters)
 					{
 						ParameterDeclaration pd = typeSystemAstBuilder.ConvertParameter(p);
-						(IProperty prop, IField field) = recordDecompiler.GetPropertyInfoByPrimaryConstructorParameter(p);
+						(IProperty? prop, IField field) = recordDecompiler.GetPropertyInfoByPrimaryConstructorParameter(p);
 
 						if (prop != null)
 						{
@@ -1567,7 +1567,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				if (MemberIsHidden(module, field.MetadataToken, settings))
 					continue;
-				object constantValue = field.GetConstantValue();
+				object? constantValue = field.GetConstantValue();
 				if (constantValue == null)
 					continue;
 				long currentValue = (long)CSharpPrimitiveCast.Cast(TypeCode.Int64, constantValue, false);
@@ -1958,7 +1958,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				if (decompilationContext.CurrentTypeDefinition.Kind == TypeKind.Enum && field.IsConst)
 				{
 					var enumDec = new EnumMemberDeclaration { Name = field.Name };
-					object constantValue = field.GetConstantValue();
+					object? constantValue = field.GetConstantValue();
 					if (constantValue != null)
 					{
 						enumDec.Initializer = typeSystemAstBuilder.ConvertConstantValue(decompilationContext.CurrentTypeDefinition.EnumUnderlyingType, constantValue);
@@ -2022,7 +2022,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			type = null;
 			elementCount = 0;
-			IAttribute attr = field.GetAttribute(KnownAttribute.FixedBuffer);
+			IAttribute? attr = field.GetAttribute(KnownAttribute.FixedBuffer);
 			if (attr != null && attr.FixedArguments.Length == 2)
 			{
 				if (attr.FixedArguments[0].Value is IType trr && attr.FixedArguments[1].Value is int length)

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -1574,7 +1574,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				arguments.Remove(value);
 			}
 
-			IMember foundMember;
+			IMember? foundMember;
 			while (!IsUnambiguousAccess(expectedTargetDetails, targetResolveResult, method, arguments, argumentNames, out foundMember))
 			{
 				if (!argumentsCasted)

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -2535,7 +2535,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (resultType.Kind == TypeKind.Void)
 				return compilation.FindType(KnownTypeCode.Task);
 
-			ITypeDefinition def = compilation.FindType(KnownTypeCode.TaskOfT).GetDefinition();
+			ITypeDefinition? def = compilation.FindType(KnownTypeCode.TaskOfT).GetDefinition();
 			if (def != null)
 				return new ParameterizedType(def, new[] { resultType });
 			else
@@ -2988,7 +2988,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				memberName = "LongLength";
 				code = KnownTypeCode.Int64;
 			}
-			IProperty member = arrayType.GetProperties(p => p.Name == memberName).FirstOrDefault();
+			IProperty? member = arrayType.GetProperties(p => p.Name == memberName).FirstOrDefault();
 			ResolveResult rr = member == null
 				? new ResolveResult(compilation.FindType(code))
 				: new MemberResolveResult(arrayExpr.ResolveResult, member);
@@ -3917,7 +3917,8 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			TranslatedExpression value;
 			IType type;
-			if (inst.Value is StringToInt strToInt)
+			var strToInt = inst.Value as StringToInt;
+			if (strToInt != null)
 			{
 				value = Translate(strToInt.Argument)
 					.ConvertTo(
@@ -4534,7 +4535,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					{
 						if (subPattern.HasDesignator)
 						{
-							if (!conversionMapping.TryGetValue(subPattern.Variable, out ILVariable value))
+							if (!conversionMapping.TryGetValue(subPattern.Variable, out ILVariable? value))
 							{
 								value = subPattern.Variable;
 							}
@@ -4639,7 +4640,7 @@ namespace ICSharpCode.Decompiler.CSharp
 								Debug.Fail("Invalid sub pattern");
 								continue;
 							}
-							IMember member;
+							IMember? member;
 							if (testedOperand is CallInstruction call)
 							{
 								member = call.Method.AccessorOwner;

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -92,7 +92,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		/// </summary>
 		/// <param name="nextNode">The next node after the comma.</param>
 		/// <param name="noSpaceAfterComma">When set prevents printing a space after comma.</param>
-		protected virtual void Comma(AstNode nextNode, bool noSpaceAfterComma = false)
+		protected virtual void Comma(AstNode? nextNode, bool noSpaceAfterComma = false)
 		{
 			Space(policy.SpaceBeforeBracketComma);
 			// TODO: Comma policy has changed.
@@ -105,7 +105,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		/// <summary>
 		/// Writes an optional comma, e.g. at the end of an enum declaration or in an array initializer
 		/// </summary>
-		protected virtual void OptionalComma(AstNode pos)
+		protected virtual void OptionalComma(AstNode? pos)
 		{
 			// Look if there's a comma after the current node, and insert it if it exists.
 			while (pos != null && pos.NodeType == NodeType.Whitespace)
@@ -121,7 +121,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		/// <summary>
 		/// Writes an optional semicolon, e.g. at the end of a type or namespace declaration.
 		/// </summary>
-		protected virtual void OptionalSemicolon(AstNode pos)
+		protected virtual void OptionalSemicolon(AstNode? pos)
 		{
 			// Look if there's a semicolon after the current node, and insert it if it exists.
 			while (pos != null && pos.NodeType == NodeType.Whitespace)
@@ -1947,7 +1947,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			WriteIdentifier(labelStatement.GetChildByRole(Roles.Identifier));
 			WriteToken(Roles.Colon);
 			bool foundLabelledStatement = false;
-			for (AstNode tmp = labelStatement.NextSibling; tmp != null; tmp = tmp.NextSibling)
+			for (AstNode? tmp = labelStatement.NextSibling; tmp != null; tmp = tmp.NextSibling)
 			{
 				if (tmp.Role == labelStatement.Role)
 				{

ICSharpCode.Decompiler/CSharp/OutputVisitor/GenericGrammarAmbiguityVisitor.cs

@@ -53,7 +53,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			var v = new GenericGrammarAmbiguityVisitor();
 			v.genericNestingLevel = 1;
 
-			for (AstNode node = binaryOperatorExpression.Right; node != null; node = node.GetNextNode())
+			for (AstNode? node = binaryOperatorExpression.Right; node != null; node = node.GetNextNode())
 			{
 				if (node.AcceptVisitor(v))
 					return v.ambiguityFound;

ICSharpCode.Decompiler/CSharp/OutputVisitor/InsertSpecialsDecorator.cs

@@ -84,7 +84,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		/// </summary>
 		void WriteSpecials(AstNode start, AstNode end)
 		{
-			for (AstNode pos = start; pos != end; pos = pos.NextSibling)
+			for (AstNode? pos = start; pos != end; pos = pos.NextSibling)
 			{
 				if (pos.Role == Roles.Comment)
 				{
@@ -125,7 +125,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				return;
 			}
 			// Look for the role between the current position and the nextNode.
-			for (AstNode pos = positionStack.Peek(); pos != null && pos != nextNode; pos = pos.NextSibling)
+			for (AstNode? pos = positionStack.Peek(); pos != null && pos != nextNode; pos = pos.NextSibling)
 			{
 				if (pos.Role == role)
 				{
@@ -149,7 +149,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			{
 				return;
 			}
-			for (AstNode pos = positionStack.Peek(); pos != null; pos = pos.NextSibling)
+			for (AstNode? pos = positionStack.Peek(); pos != null; pos = pos.NextSibling)
 			{
 				if (pos == node)
 				{

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/ProjectFileWriterSdkStyle.cs

@@ -272,7 +272,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 
 			foreach (var reference in module.AssemblyReferences.Where(r => !ImplicitReferences.Contains(r.Name)))
 			{
-				if (isNetCoreApp && project.AssemblyReferenceClassifier.IsSharedAssembly(reference, out string runtimePack) && targetPacks.Contains(runtimePack))
+				if (isNetCoreApp && project.AssemblyReferenceClassifier.IsSharedAssembly(reference, out string? runtimePack) && targetPacks.Contains(runtimePack))
 				{
 					continue;
 				}

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/TargetFramework.cs

@@ -52,7 +52,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 		/// <summary>
 		/// Gets the target framework identifier. Can be null if not defined.
 		/// </summary>
-		public string Identifier { get; }
+		public string? Identifier { get; }
 
 		/// <summary>
 		/// Gets the target framework moniker. Can be null if not supported.

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/TargetServices.cs

@@ -74,7 +74,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 			{
 				string[] frameworkParts = targetFramework.Split(',');
 				targetFrameworkIdentifier = frameworkParts.FirstOrDefault(a => !a.StartsWith(VersionToken, StringComparison.OrdinalIgnoreCase) && !a.StartsWith(ProfileToken, StringComparison.OrdinalIgnoreCase));
-				string frameworkVersion = frameworkParts.FirstOrDefault(a => a.StartsWith(VersionToken, StringComparison.OrdinalIgnoreCase));
+				string? frameworkVersion = frameworkParts.FirstOrDefault(a => a.StartsWith(VersionToken, StringComparison.OrdinalIgnoreCase));
 
 				if (frameworkVersion != null)
 				{
@@ -83,7 +83,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 						versionNumber *= 10;
 				}
 
-				string frameworkProfile = frameworkParts.FirstOrDefault(a => a.StartsWith(ProfileToken, StringComparison.OrdinalIgnoreCase));
+				string? frameworkProfile = frameworkParts.FirstOrDefault(a => a.StartsWith(ProfileToken, StringComparison.OrdinalIgnoreCase));
 				if (frameworkProfile != null)
 					targetFrameworkProfile = frameworkProfile.Substring(ProfileToken.Length);
 			}

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs

@@ -325,7 +325,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 		{
 			foreach (var r in module.Resources.Where(r => r.ResourceType == ResourceType.Embedded))
 			{
-				Stream stream = r.TryOpenStream();
+				Stream? stream = r.TryOpenStream();
 				stream.Position = 0;
 
 				if (r.Name.EndsWith(".resources", StringComparison.OrdinalIgnoreCase))
@@ -341,7 +341,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 							{
 								string fileName = SanitizeFileName(name)
 									.Replace('/', Path.DirectorySeparatorChar);
-								string dirName = Path.GetDirectoryName(fileName);
+								string? dirName = Path.GetDirectoryName(fileName);
 								if (!string.IsNullOrEmpty(dirName) && directories.Add(dirName))
 								{
 									Directory.CreateDirectory(Path.Combine(TargetDirectory, dirName));

ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs

@@ -37,7 +37,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			var collector = new RequiredNamespaceCollector(namespaces);
 			foreach (var type in module.TypeDefinitions)
 			{
-				collector.CollectNamespaces(type, module, (CodeMappingInfo)null);
+				collector.CollectNamespaces(type, module, (CodeMappingInfo?)null);
 			}
 			collector.HandleAttributes(module.GetAssemblyAttributes());
 			collector.HandleAttributes(module.GetModuleAttributes());

ICSharpCode.Decompiler/CSharp/Resolver/CSharpConversions.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			if (compilation == null)
 				throw new ArgumentNullException(nameof(compilation));
 			CacheManager cache = compilation.CacheManager;
-			CSharpConversions operators = (CSharpConversions)cache.GetShared(typeof(CSharpConversions));
+			CSharpConversions? operators = (CSharpConversions)cache.GetShared(typeof(CSharpConversions));
 			if (operators == null)
 			{
 				operators = (CSharpConversions)cache.GetOrAddShared(typeof(CSharpConversions), new CSharpConversions(compilation));
@@ -182,7 +182,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				throw new ArgumentNullException(nameof(toType));
 
 			TypePair pair = new TypePair(fromType, toType);
-			if (implicitConversionCache.TryGetValue(pair, out Conversion c))
+			if (implicitConversionCache.TryGetValue(pair, out Conversion? c))
 				return c;
 
 			c = ImplicitConversion(fromType, toType, allowUserDefined: true, allowTuple: true);
@@ -600,7 +600,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 		bool IdentityOrVarianceConversion(IType s, IType t, int subtypeCheckNestingDepth)
 		{
-			ITypeDefinition def = s.GetDefinition();
+			ITypeDefinition? def = s.GetDefinition();
 			if (def != null)
 			{
 				if (!def.Equals(t.GetDefinition()))
@@ -697,7 +697,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 			else if (fromType.Kind == TypeKind.Delegate && toType.Kind == TypeKind.Delegate)
 			{
-				ITypeDefinition def = fromType.GetDefinition();
+				ITypeDefinition? def = fromType.GetDefinition();
 				if (def == null || !def.Equals(toType.GetDefinition()))
 					return false;
 				ParameterizedType? ps = fromType as ParameterizedType;
@@ -811,7 +811,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 			else if (fromTypeCode == TypeCode.Int32)
 			{
-				object cv = rr.ConstantValue;
+				object? cv = rr.ConstantValue;
 				if (cv == null)
 					return false;
 				int val = (int)cv;

ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs

@@ -506,7 +506,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 			else if (expression.IsCompileTimeConstant && m.CanEvaluateAtCompileTime)
 			{
-				object val;
+				object? val;
 				try
 				{
 					val = m.Invoke(this, expression.ConstantValue);
@@ -923,7 +923,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 			else if (lhs.IsCompileTimeConstant && rhs.IsCompileTimeConstant && m.CanEvaluateAtCompileTime)
 			{
-				object val;
+				object? val;
 				try
 				{
 					val = m.Invoke(this, lhs.ConstantValue, rhs.ConstantValue);
@@ -982,7 +982,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		#region Enum helper methods
 		IType GetEnumUnderlyingType(IType enumType)
 		{
-			ITypeDefinition def = enumType.GetDefinition();
+			ITypeDefinition? def = enumType.GetDefinition();
 			return def != null ? def.EnumUnderlyingType : SpecialType.UnknownType;
 		}
 
@@ -1609,12 +1609,12 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return trr != null && trr.Type.Equals(rr.Type);
 		}
 
-		ResolveResult LookInCurrentType(string identifier, IReadOnlyList<IType> typeArguments, NameLookupMode lookupMode, bool parameterizeResultType)
+		ResolveResult? LookInCurrentType(string identifier, IReadOnlyList<IType> typeArguments, NameLookupMode lookupMode, bool parameterizeResultType)
 		{
 			int k = typeArguments.Count;
 			MemberLookup lookup = CreateMemberLookup(lookupMode);
 			// look in current type definitions
-			for (ITypeDefinition t = this.CurrentTypeDefinition; t != null; t = t.DeclaringTypeDefinition)
+			for (ITypeDefinition? t = this.CurrentTypeDefinition; t != null; t = t.DeclaringTypeDefinition)
 			{
 				if (k == 0)
 				{
@@ -1651,7 +1651,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return null;
 		}
 
-		ResolveResult LookInCurrentUsingScope(string identifier, IReadOnlyList<IType> typeArguments, bool isInUsingDeclaration, bool parameterizeResultType)
+		ResolveResult? LookInCurrentUsingScope(string identifier, IReadOnlyList<IType> typeArguments, bool isInUsingDeclaration, bool parameterizeResultType)
 		{
 			// look in current namespace definitions
 			ResolvedUsingScope currentUsingScope = this.CurrentUsingScope;
@@ -1684,7 +1684,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					IType? firstResult = null;
 					foreach (var importedNamespace in u.Usings)
 					{
-						ITypeDefinition def = importedNamespace.GetTypeDefinition(identifier, typeArguments.Count);
+						ITypeDefinition? def = importedNamespace.GetTypeDefinition(identifier, typeArguments.Count);
 						if (def != null)
 						{
 							IType resultType;
@@ -1712,7 +1712,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return null;
 		}
 
-		ResolveResult LookInUsingScopeNamespace(ResolvedUsingScope usingScope, INamespace n, string identifier, IReadOnlyList<IType> typeArguments, bool parameterizeResultType)
+		ResolveResult? LookInUsingScopeNamespace(ResolvedUsingScope usingScope, INamespace n, string identifier, IReadOnlyList<IType> typeArguments, bool parameterizeResultType)
 		{
 			if (n == null)
 				return null;
@@ -1720,7 +1720,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			int k = typeArguments.Count;
 			if (k == 0)
 			{
-				INamespace childNamespace = n.GetChildNamespace(identifier);
+				INamespace? childNamespace = n.GetChildNamespace(identifier);
 				if (childNamespace != null)
 				{
 					if (usingScope != null && usingScope.HasAlias(identifier))
@@ -1729,7 +1729,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				}
 			}
 			// then look for a type
-			ITypeDefinition def = n.GetTypeDefinition(identifier, k);
+			ITypeDefinition? def = n.GetTypeDefinition(identifier, k);
 			if (def != null && TopLevelTypeDefinitionIsAccessible(def))
 			{
 				IType result = def;
@@ -1781,7 +1781,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 		ResolveResult ResolveExternAlias(string alias)
 		{
-			INamespace ns = compilation.GetNamespaceForExternAlias(alias);
+			INamespace? ns = compilation.GetNamespaceForExternAlias(alias);
 			if (ns != null)
 				return new NamespaceResolveResult(ns);
 			else
@@ -1854,11 +1854,11 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		{
 			if (typeArguments.Count == 0)
 			{
-				INamespace childNamespace = nrr.Namespace.GetChildNamespace(identifier);
+				INamespace? childNamespace = nrr.Namespace.GetChildNamespace(identifier);
 				if (childNamespace != null)
 					return new NamespaceResolveResult(childNamespace);
 			}
-			ITypeDefinition def = nrr.Namespace.GetTypeDefinition(identifier, typeArguments.Count);
+			ITypeDefinition? def = nrr.Namespace.GetTypeDefinition(identifier, typeArguments.Count);
 			if (def != null)
 			{
 				if (parameterizeResultType && typeArguments.Count > 0)
@@ -1985,13 +1985,13 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			elementType = expression.Type.GetElementTypeFromIEnumerable(compilation, false, out bool? isGeneric);
 			if (isGeneric == true)
 			{
-				ITypeDefinition enumerableOfT = compilation.FindType(KnownTypeCode.IEnumerableOfT).GetDefinition();
+				ITypeDefinition? enumerableOfT = compilation.FindType(KnownTypeCode.IEnumerableOfT).GetDefinition();
 				if (enumerableOfT != null)
 					collectionType = new ParameterizedType(enumerableOfT, new[] { elementType });
 				else
 					collectionType = SpecialType.UnknownType;
 
-				ITypeDefinition enumeratorOfT = compilation.FindType(KnownTypeCode.IEnumeratorOfT).GetDefinition();
+				ITypeDefinition? enumeratorOfT = compilation.FindType(KnownTypeCode.IEnumeratorOfT).GetDefinition();
 				if (enumeratorOfT != null)
 					enumeratorType = new ParameterizedType(enumeratorOfT, new[] { elementType });
 				else
@@ -2060,7 +2060,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		///    new List { all extensions from SomeExtensions }
 		/// }
 		/// </remarks>
-		public List<List<IMethod>> GetExtensionMethods(IType targetType, string? name = null, IReadOnlyList<IType>? typeArguments = null, bool substituteInferredTypes = false)
+		public List<List<IMethod>> GetExtensionMethods(IType? targetType, string? name = null, IReadOnlyList<IType>? typeArguments = null, bool substituteInferredTypes = false)
 		{
 			var lookup = CreateMemberLookup();
 			List<List<IMethod>> extensionMethodGroups = new List<List<IMethod>>();
@@ -2073,7 +2073,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 						continue;
 					if (!lookup.IsAccessible(method, false))
 						continue;
-					IType[] inferredTypes;
+					IType[]? inferredTypes;
 					if (typeArguments != null && typeArguments.Count > 0)
 					{
 						if (method.TypeParameters.Count != typeArguments.Count)
@@ -2118,7 +2118,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// If an array is returned, any slot with an uninferred type argument will be set to the method's
 		/// corresponding type parameter.
 		/// </param>
-		public static bool IsEligibleExtensionMethod(IType targetType, IMethod method, bool useTypeInference, out IType[] outInferredTypes)
+		public static bool IsEligibleExtensionMethod(IType targetType, IMethod method, bool useTypeInference, out IType[]? outInferredTypes)
 		{
 			if (targetType == null)
 				throw new ArgumentNullException(nameof(targetType));
@@ -2128,7 +2128,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return IsEligibleExtensionMethod(compilation, CSharpConversions.Get(compilation), targetType, method, useTypeInference, out outInferredTypes);
 		}
 
-		static bool IsEligibleExtensionMethod(ICompilation compilation, CSharpConversions conversions, IType targetType, IMethod method, bool useTypeInference, out IType[]? outInferredTypes)
+		static bool IsEligibleExtensionMethod(ICompilation compilation, CSharpConversions conversions, IType? targetType, IMethod method, bool useTypeInference, out IType[]? outInferredTypes)
 		{
 			outInferredTypes = null;
 			if (targetType == null)
@@ -2814,9 +2814,9 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return new ConstantResolveResult(type, GetDefaultValue(type));
 		}
 
-		public static object GetDefaultValue(IType type)
+		public static object? GetDefaultValue(IType type)
 		{
-			ITypeDefinition typeDef = type.GetDefinition();
+			ITypeDefinition? typeDef = type.GetDefinition();
 			if (typeDef == null)
 				return null;
 			if (typeDef.Kind == TypeKind.Enum)

ICSharpCode.Decompiler/CSharp/Resolver/MemberLookup.cs

@@ -79,7 +79,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		{
 			if (targetType.Kind == TypeKind.TypeParameter)
 				targetType = ((ITypeParameter)targetType).EffectiveBaseClass;
-			ITypeDefinition typeDef = targetType.GetDefinition();
+			ITypeDefinition? typeDef = targetType.GetDefinition();
 			if (typeDef == null)
 				return false;
 			for (ITypeDefinition c = currentTypeDefinition; c != null; c = c.DeclaringTypeDefinition)
@@ -195,7 +195,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				foreach (var entityGroup in entities.GroupBy(e => e.Name))
 				{
 
-					List<LookupGroup> lookupGroups = new List<LookupGroup>();
+					List<LookupGroup>? lookupGroups = new List<LookupGroup>();
 					if (!lookupGroupDict.TryGetValue(entityGroup.Key, out lookupGroups))
 						lookupGroupDict.Add(entityGroup.Key, lookupGroups = new List<LookupGroup>());
 
@@ -243,7 +243,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					{
 						foreach (IType type in lookupGroup.NestedTypes)
 						{
-							ITypeDefinition typeDef = type.GetDefinition();
+							ITypeDefinition? typeDef = type.GetDefinition();
 							if (typeDef != null)
 								yield return typeDef;
 						}
@@ -691,7 +691,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			// return true if type is an interface or System.Object
 			if (type.Kind == TypeKind.Interface)
 				return true;
-			ITypeDefinition d = type.GetDefinition();
+			ITypeDefinition? d = type.GetDefinition();
 			return d != null && d.KnownTypeCode == KnownTypeCode.Object;
 		}
 		#endregion

ICSharpCode.Decompiler/CSharp/Resolver/OverloadResolution.cs

@@ -582,7 +582,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 			if (typeParameter.HasDefaultConstructorConstraint)
 			{
-				ITypeDefinition def = typeArgument.GetDefinition();
+				ITypeDefinition? def = typeArgument.GetDefinition();
 				if (def != null && def.IsAbstract)
 					return false;
 				var ctors = typeArgument.GetConstructors(

ICSharpCode.Decompiler/CSharp/Resolver/TypeInference.cs

@@ -1109,7 +1109,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			// Now filter out candidates that violate the upper bounds:
 			foreach (IType ub in upperBounds)
 			{
-				ITypeDefinition ubDef = ub.GetDefinition();
+				ITypeDefinition? ubDef = ub.GetDefinition();
 				if (ubDef != null)
 				{
 					candidateTypeDefinitions.RemoveAll(c => !c.IsDerivedFrom(ubDef));

ICSharpCode.Decompiler/CSharp/SequencePointBuilder.cs

@@ -547,7 +547,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 
 
-				List<int> sequencePointCandidates = function.SequencePointCandidates;
+				List<int>? sequencePointCandidates = function.SequencePointCandidates;
 				int currSPCandidateIndex = 0;
 
 				for (int i = 0; i < newList.Count - 1; i++)

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -213,7 +213,8 @@ namespace ICSharpCode.Decompiler.CSharp
 
 			TranslatedExpression value;
 			IType type;
-			if (inst.Value is StringToInt strToInt)
+			var strToInt = inst.Value as StringToInt;
+			if (strToInt != null)
 			{
 				value = exprBuilder.Translate(strToInt.Argument)
 					.ConvertTo(
@@ -328,7 +329,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					}
 					Debug.Assert(block.FinalInstruction.OpCode == OpCode.Nop);
 				}
-				if (endContainerLabels.TryGetValue(switchContainer, out string label))
+				if (endContainerLabels.TryGetValue(switchContainer, out string? label))
 				{
 					lastSectionStatements.Add(new LabelStatement { Label = label });
 					lastSectionStatements.Add(new BreakStatement());
@@ -411,7 +412,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				else
 					return new ReturnStatement().WithILInstruction(inst);
 			}
-			if (!endContainerLabels.TryGetValue(inst.TargetContainer, out string label))
+			if (!endContainerLabels.TryGetValue(inst.TargetContainer, out string? label))
 			{
 				label = "end_" + inst.TargetLabel;
 				if (!duplicateLabels.TryGetValue(label, out int count))
@@ -1261,8 +1262,8 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		Statement ConvertLoop(BlockContainer container)
 		{
-			ILInstruction condition;
-			Block loopBody;
+			ILInstruction? condition;
+			Block? loopBody;
 			BlockStatement blockStatement;
 			continueCount = 0;
 			breakTarget = container;
@@ -1480,7 +1481,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					blockStatement.Add(Convert(block.FinalInstruction));
 				}
 			}
-			if (endContainerLabels.TryGetValue(container, out string label))
+			if (endContainerLabels.TryGetValue(container, out string? label))
 			{
 				if (isLoop && !(blockStatement.LastOrDefault() is ContinueStatement))
 				{
@@ -1500,7 +1501,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		string EnsureUniqueLabel(Block block)
 		{
-			if (labels.TryGetValue(block, out string label))
+			if (labels.TryGetValue(block, out string? label))
 				return label;
 			if (!duplicateLabels.TryGetValue(block.Label, out int count))
 			{

ICSharpCode.Decompiler/CSharp/Syntax/AstNode.cs

@@ -202,7 +202,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			get { return parent; }
 		}
 
-		public Role Role {
+		public Role? Role {
 			get {
 				return Role.GetByIndex(flags & roleIndexMask);
 			}

ICSharpCode.Decompiler/CSharp/Syntax/AstNodeCollection.cs

@@ -49,7 +49,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			get {
 				int count = 0;
 				uint roleIndex = role.Index;
-				for (AstNode cur = node.FirstChild; cur != null; cur = cur.NextSibling)
+				for (AstNode? cur = node.FirstChild; cur != null; cur = cur.NextSibling)
 				{
 					if (cur.RoleIndex == roleIndex)
 						count++;
@@ -177,8 +177,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public IEnumerator<T> GetEnumerator()
 		{
 			uint roleIndex = role.Index;
-			AstNode next;
-			for (AstNode cur = node.FirstChild; cur != null; cur = next)
+			AstNode? next;
+			for (AstNode? cur = node.FirstChild; cur != null; cur = next)
 			{
 				Debug.Assert(cur.Parent == node);
 				// Remember next before yielding cur.
@@ -214,7 +214,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return Pattern.DoMatchCollection(role, node.FirstChild, other.node.FirstChild, match);
 		}
 
-		public void InsertAfter(T existingItem, T newItem)
+		public void InsertAfter(T? existingItem, T newItem)
 		{
 			node.InsertChildAfter(existingItem, newItem, role);
 		}
@@ -230,8 +230,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public void AcceptVisitor(IAstVisitor visitor)
 		{
 			uint roleIndex = role.Index;
-			AstNode next;
-			for (AstNode cur = node.FirstChild; cur != null; cur = next)
+			AstNode? next;
+			for (AstNode? cur = node.FirstChild; cur != null; cur = next)
 			{
 				Debug.Assert(cur.Parent == node);
 				// Remember next before yielding cur.

ICSharpCode.Decompiler/CSharp/Syntax/DepthFirstAstVisitor.cs

@@ -34,7 +34,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	{
 		protected virtual void VisitChildren(AstNode node)
 		{
-			AstNode next;
+			AstNode? next;
 			for (var child = node.FirstChild; child != null; child = next)
 			{
 				// Store next to allow the loop to continue
@@ -715,7 +715,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	{
 		protected virtual T VisitChildren(AstNode node)
 		{
-			AstNode next;
+			AstNode? next;
 			for (var child = node.FirstChild; child != null; child = next)
 			{
 				// Store next to allow the loop to continue
@@ -1396,9 +1396,9 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	/// </summary>
 	public abstract class DepthFirstAstVisitor<T, S> : IAstVisitor<T, S>
 	{
-		protected virtual S VisitChildren(AstNode node, T data)
+		protected virtual S? VisitChildren(AstNode node, T data)
 		{
-			AstNode next;
+			AstNode? next;
 			for (var child = node.FirstChild; child != null; child = next)
 			{
 				// Store next to allow the loop to continue
@@ -1409,7 +1409,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return default(S);
 		}
 
-		public virtual S VisitNullNode(AstNode nullNode, T data)
+		public virtual S? VisitNullNode(AstNode nullNode, T data)
 		{
 			// Should we call VisitChildren here?
 			// We usually want to ignore null nodes.
@@ -1418,657 +1418,657 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return default(S);
 		}
 
-		public virtual S VisitSyntaxTree(SyntaxTree unit, T data)
+		public virtual S? VisitSyntaxTree(SyntaxTree unit, T data)
 		{
 			return VisitChildren(unit, data);
 		}
 
-		public virtual S VisitComment(Comment comment, T data)
+		public virtual S? VisitComment(Comment comment, T data)
 		{
 			return VisitChildren(comment, data);
 		}
 
-		public virtual S VisitDocumentationReference(DocumentationReference documentationReference, T data)
+		public virtual S? VisitDocumentationReference(DocumentationReference documentationReference, T data)
 		{
 			return VisitChildren(documentationReference, data);
 		}
 
-		public virtual S VisitPreProcessorDirective(PreProcessorDirective preProcessorDirective, T data)
+		public virtual S? VisitPreProcessorDirective(PreProcessorDirective preProcessorDirective, T data)
 		{
 			return VisitChildren(preProcessorDirective, data);
 		}
 
-		public virtual S VisitIdentifier(Identifier identifier, T data)
+		public virtual S? VisitIdentifier(Identifier identifier, T data)
 		{
 			return VisitChildren(identifier, data);
 		}
 
-		public virtual S VisitCSharpTokenNode(CSharpTokenNode token, T data)
+		public virtual S? VisitCSharpTokenNode(CSharpTokenNode token, T data)
 		{
 			return VisitChildren(token, data);
 		}
 
-		public virtual S VisitPrimitiveType(PrimitiveType primitiveType, T data)
+		public virtual S? VisitPrimitiveType(PrimitiveType primitiveType, T data)
 		{
 			return VisitChildren(primitiveType, data);
 		}
 
-		public virtual S VisitComposedType(ComposedType composedType, T data)
+		public virtual S? VisitComposedType(ComposedType composedType, T data)
 		{
 			return VisitChildren(composedType, data);
 		}
 
-		public virtual S VisitSimpleType(SimpleType simpleType, T data)
+		public virtual S? VisitSimpleType(SimpleType simpleType, T data)
 		{
 			return VisitChildren(simpleType, data);
 		}
 
-		public virtual S VisitMemberType(MemberType memberType, T data)
+		public virtual S? VisitMemberType(MemberType memberType, T data)
 		{
 			return VisitChildren(memberType, data);
 		}
 
-		public virtual S VisitTupleType(TupleAstType tupleType, T data)
+		public virtual S? VisitTupleType(TupleAstType tupleType, T data)
 		{
 			return VisitChildren(tupleType, data);
 		}
 
-		public virtual S VisitTupleTypeElement(TupleTypeElement tupleTypeElement, T data)
+		public virtual S? VisitTupleTypeElement(TupleTypeElement tupleTypeElement, T data)
 		{
 			return VisitChildren(tupleTypeElement, data);
 		}
 
-		public virtual S VisitFunctionPointerType(FunctionPointerAstType functionPointerType, T data)
+		public virtual S? VisitFunctionPointerType(FunctionPointerAstType functionPointerType, T data)
 		{
 			return VisitChildren(functionPointerType, data);
 		}
 
-		public virtual S VisitInvocationType(InvocationAstType invocationType, T data)
+		public virtual S? VisitInvocationType(InvocationAstType invocationType, T data)
 		{
 			return VisitChildren(invocationType, data);
 		}
 
-		public virtual S VisitAttribute(Attribute attribute, T data)
+		public virtual S? VisitAttribute(Attribute attribute, T data)
 		{
 			return VisitChildren(attribute, data);
 		}
 
-		public virtual S VisitAttributeSection(AttributeSection attributeSection, T data)
+		public virtual S? VisitAttributeSection(AttributeSection attributeSection, T data)
 		{
 			return VisitChildren(attributeSection, data);
 		}
 
-		public virtual S VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration, T data)
+		public virtual S? VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration, T data)
 		{
 			return VisitChildren(delegateDeclaration, data);
 		}
 
-		public virtual S VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration, T data)
+		public virtual S? VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration, T data)
 		{
 			return VisitChildren(namespaceDeclaration, data);
 		}
 
-		public virtual S VisitTypeDeclaration(TypeDeclaration typeDeclaration, T data)
+		public virtual S? VisitTypeDeclaration(TypeDeclaration typeDeclaration, T data)
 		{
 			return VisitChildren(typeDeclaration, data);
 		}
 
-		public virtual S VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration, T data)
+		public virtual S? VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration, T data)
 		{
 			return VisitChildren(typeParameterDeclaration, data);
 		}
 
-		public virtual S VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration, T data)
+		public virtual S? VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration, T data)
 		{
 			return VisitChildren(enumMemberDeclaration, data);
 		}
 
-		public virtual S VisitUsingDeclaration(UsingDeclaration usingDeclaration, T data)
+		public virtual S? VisitUsingDeclaration(UsingDeclaration usingDeclaration, T data)
 		{
 			return VisitChildren(usingDeclaration, data);
 		}
 
-		public virtual S VisitUsingAliasDeclaration(UsingAliasDeclaration usingDeclaration, T data)
+		public virtual S? VisitUsingAliasDeclaration(UsingAliasDeclaration usingDeclaration, T data)
 		{
 			return VisitChildren(usingDeclaration, data);
 		}
 
-		public virtual S VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration, T data)
+		public virtual S? VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration, T data)
 		{
 			return VisitChildren(externAliasDeclaration, data);
 		}
 
-		public virtual S VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration, T data)
+		public virtual S? VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration, T data)
 		{
 			return VisitChildren(constructorDeclaration, data);
 		}
 
-		public virtual S VisitConstructorInitializer(ConstructorInitializer constructorInitializer, T data)
+		public virtual S? VisitConstructorInitializer(ConstructorInitializer constructorInitializer, T data)
 		{
 			return VisitChildren(constructorInitializer, data);
 		}
 
-		public virtual S VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration, T data)
+		public virtual S? VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration, T data)
 		{
 			return VisitChildren(destructorDeclaration, data);
 		}
 
-		public virtual S VisitEventDeclaration(EventDeclaration eventDeclaration, T data)
+		public virtual S? VisitEventDeclaration(EventDeclaration eventDeclaration, T data)
 		{
 			return VisitChildren(eventDeclaration, data);
 		}
 
-		public virtual S VisitCustomEventDeclaration(CustomEventDeclaration eventDeclaration, T data)
+		public virtual S? VisitCustomEventDeclaration(CustomEventDeclaration eventDeclaration, T data)
 		{
 			return VisitChildren(eventDeclaration, data);
 		}
 
-		public virtual S VisitFieldDeclaration(FieldDeclaration fieldDeclaration, T data)
+		public virtual S? VisitFieldDeclaration(FieldDeclaration fieldDeclaration, T data)
 		{
 			return VisitChildren(fieldDeclaration, data);
 		}
 
-		public virtual S VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration, T data)
+		public virtual S? VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration, T data)
 		{
 			return VisitChildren(fixedFieldDeclaration, data);
 		}
 
-		public virtual S VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer, T data)
+		public virtual S? VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer, T data)
 		{
 			return VisitChildren(fixedVariableInitializer, data);
 		}
 
-		public virtual S VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration, T data)
+		public virtual S? VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration, T data)
 		{
 			return VisitChildren(indexerDeclaration, data);
 		}
 
-		public virtual S VisitMethodDeclaration(MethodDeclaration methodDeclaration, T data)
+		public virtual S? VisitMethodDeclaration(MethodDeclaration methodDeclaration, T data)
 		{
 			return VisitChildren(methodDeclaration, data);
 		}
 
-		public virtual S VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration, T data)
+		public virtual S? VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration, T data)
 		{
 			return VisitChildren(operatorDeclaration, data);
 		}
 
-		public virtual S VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration, T data)
+		public virtual S? VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration, T data)
 		{
 			return VisitChildren(propertyDeclaration, data);
 		}
 
-		public virtual S VisitAccessor(Accessor accessor, T data)
+		public virtual S? VisitAccessor(Accessor accessor, T data)
 		{
 			return VisitChildren(accessor, data);
 		}
 
-		public virtual S VisitVariableInitializer(VariableInitializer variableInitializer, T data)
+		public virtual S? VisitVariableInitializer(VariableInitializer variableInitializer, T data)
 		{
 			return VisitChildren(variableInitializer, data);
 		}
 
-		public virtual S VisitParameterDeclaration(ParameterDeclaration parameterDeclaration, T data)
+		public virtual S? VisitParameterDeclaration(ParameterDeclaration parameterDeclaration, T data)
 		{
 			return VisitChildren(parameterDeclaration, data);
 		}
 
-		public virtual S VisitConstraint(Constraint constraint, T data)
+		public virtual S? VisitConstraint(Constraint constraint, T data)
 		{
 			return VisitChildren(constraint, data);
 		}
 
-		public virtual S VisitBlockStatement(BlockStatement blockStatement, T data)
+		public virtual S? VisitBlockStatement(BlockStatement blockStatement, T data)
 		{
 			return VisitChildren(blockStatement, data);
 		}
 
-		public virtual S VisitExpressionStatement(ExpressionStatement expressionStatement, T data)
+		public virtual S? VisitExpressionStatement(ExpressionStatement expressionStatement, T data)
 		{
 			return VisitChildren(expressionStatement, data);
 		}
 
-		public virtual S VisitBreakStatement(BreakStatement breakStatement, T data)
+		public virtual S? VisitBreakStatement(BreakStatement breakStatement, T data)
 		{
 			return VisitChildren(breakStatement, data);
 		}
 
-		public virtual S VisitCheckedStatement(CheckedStatement checkedStatement, T data)
+		public virtual S? VisitCheckedStatement(CheckedStatement checkedStatement, T data)
 		{
 			return VisitChildren(checkedStatement, data);
 		}
 
-		public virtual S VisitContinueStatement(ContinueStatement continueStatement, T data)
+		public virtual S? VisitContinueStatement(ContinueStatement continueStatement, T data)
 		{
 			return VisitChildren(continueStatement, data);
 		}
 
-		public virtual S VisitDoWhileStatement(DoWhileStatement doWhileStatement, T data)
+		public virtual S? VisitDoWhileStatement(DoWhileStatement doWhileStatement, T data)
 		{
 			return VisitChildren(doWhileStatement, data);
 		}
 
-		public virtual S VisitEmptyStatement(EmptyStatement emptyStatement, T data)
+		public virtual S? VisitEmptyStatement(EmptyStatement emptyStatement, T data)
 		{
 			return VisitChildren(emptyStatement, data);
 		}
 
-		public virtual S VisitFixedStatement(FixedStatement fixedStatement, T data)
+		public virtual S? VisitFixedStatement(FixedStatement fixedStatement, T data)
 		{
 			return VisitChildren(fixedStatement, data);
 		}
 
-		public virtual S VisitForeachStatement(ForeachStatement foreachStatement, T data)
+		public virtual S? VisitForeachStatement(ForeachStatement foreachStatement, T data)
 		{
 			return VisitChildren(foreachStatement, data);
 		}
 
-		public virtual S VisitForStatement(ForStatement forStatement, T data)
+		public virtual S? VisitForStatement(ForStatement forStatement, T data)
 		{
 			return VisitChildren(forStatement, data);
 		}
 
-		public virtual S VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement, T data)
+		public virtual S? VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement, T data)
 		{
 			return VisitChildren(gotoCaseStatement, data);
 		}
 
-		public virtual S VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement, T data)
+		public virtual S? VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement, T data)
 		{
 			return VisitChildren(gotoDefaultStatement, data);
 		}
 
-		public virtual S VisitGotoStatement(GotoStatement gotoStatement, T data)
+		public virtual S? VisitGotoStatement(GotoStatement gotoStatement, T data)
 		{
 			return VisitChildren(gotoStatement, data);
 		}
 
-		public virtual S VisitIfElseStatement(IfElseStatement ifElseStatement, T data)
+		public virtual S? VisitIfElseStatement(IfElseStatement ifElseStatement, T data)
 		{
 			return VisitChildren(ifElseStatement, data);
 		}
 
-		public virtual S VisitLabelStatement(LabelStatement labelStatement, T data)
+		public virtual S? VisitLabelStatement(LabelStatement labelStatement, T data)
 		{
 			return VisitChildren(labelStatement, data);
 		}
 
-		public virtual S VisitLockStatement(LockStatement lockStatement, T data)
+		public virtual S? VisitLockStatement(LockStatement lockStatement, T data)
 		{
 			return VisitChildren(lockStatement, data);
 		}
 
-		public virtual S VisitReturnStatement(ReturnStatement returnStatement, T data)
+		public virtual S? VisitReturnStatement(ReturnStatement returnStatement, T data)
 		{
 			return VisitChildren(returnStatement, data);
 		}
 
-		public virtual S VisitSwitchStatement(SwitchStatement switchStatement, T data)
+		public virtual S? VisitSwitchStatement(SwitchStatement switchStatement, T data)
 		{
 			return VisitChildren(switchStatement, data);
 		}
 
-		public virtual S VisitSwitchSection(SwitchSection switchSection, T data)
+		public virtual S? VisitSwitchSection(SwitchSection switchSection, T data)
 		{
 			return VisitChildren(switchSection, data);
 		}
 
-		public virtual S VisitCaseLabel(CaseLabel caseLabel, T data)
+		public virtual S? VisitCaseLabel(CaseLabel caseLabel, T data)
 		{
 			return VisitChildren(caseLabel, data);
 		}
 
-		public virtual S VisitSwitchExpression(SwitchExpression switchExpression, T data)
+		public virtual S? VisitSwitchExpression(SwitchExpression switchExpression, T data)
 		{
 			return VisitChildren(switchExpression, data);
 		}
 
-		public virtual S VisitSwitchExpressionSection(SwitchExpressionSection switchExpressionSection, T data)
+		public virtual S? VisitSwitchExpressionSection(SwitchExpressionSection switchExpressionSection, T data)
 		{
 			return VisitChildren(switchExpressionSection, data);
 		}
 
-		public virtual S VisitThrowStatement(ThrowStatement throwStatement, T data)
+		public virtual S? VisitThrowStatement(ThrowStatement throwStatement, T data)
 		{
 			return VisitChildren(throwStatement, data);
 		}
 
-		public virtual S VisitTryCatchStatement(TryCatchStatement tryCatchStatement, T data)
+		public virtual S? VisitTryCatchStatement(TryCatchStatement tryCatchStatement, T data)
 		{
 			return VisitChildren(tryCatchStatement, data);
 		}
 
-		public virtual S VisitCatchClause(CatchClause catchClause, T data)
+		public virtual S? VisitCatchClause(CatchClause catchClause, T data)
 		{
 			return VisitChildren(catchClause, data);
 		}
 
-		public virtual S VisitUncheckedStatement(UncheckedStatement uncheckedStatement, T data)
+		public virtual S? VisitUncheckedStatement(UncheckedStatement uncheckedStatement, T data)
 		{
 			return VisitChildren(uncheckedStatement, data);
 		}
 
-		public virtual S VisitUnsafeStatement(UnsafeStatement unsafeStatement, T data)
+		public virtual S? VisitUnsafeStatement(UnsafeStatement unsafeStatement, T data)
 		{
 			return VisitChildren(unsafeStatement, data);
 		}
 
-		public virtual S VisitUsingStatement(UsingStatement usingStatement, T data)
+		public virtual S? VisitUsingStatement(UsingStatement usingStatement, T data)
 		{
 			return VisitChildren(usingStatement, data);
 		}
 
-		public virtual S VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement, T data)
+		public virtual S? VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement, T data)
 		{
 			return VisitChildren(variableDeclarationStatement, data);
 		}
 
-		public virtual S VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement, T data)
+		public virtual S? VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement, T data)
 		{
 			return VisitChildren(localFunctionDeclarationStatement, data);
 		}
 
-		public virtual S VisitWhileStatement(WhileStatement whileStatement, T data)
+		public virtual S? VisitWhileStatement(WhileStatement whileStatement, T data)
 		{
 			return VisitChildren(whileStatement, data);
 		}
 
-		public virtual S VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement, T data)
+		public virtual S? VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement, T data)
 		{
 			return VisitChildren(yieldBreakStatement, data);
 		}
 
-		public virtual S VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement, T data)
+		public virtual S? VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement, T data)
 		{
 			return VisitChildren(yieldReturnStatement, data);
 		}
 
-		public virtual S VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression, T data)
+		public virtual S? VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression, T data)
 		{
 			return VisitChildren(anonymousMethodExpression, data);
 		}
 
-		public virtual S VisitLambdaExpression(LambdaExpression lambdaExpression, T data)
+		public virtual S? VisitLambdaExpression(LambdaExpression lambdaExpression, T data)
 		{
 			return VisitChildren(lambdaExpression, data);
 		}
 
-		public virtual S VisitAssignmentExpression(AssignmentExpression assignmentExpression, T data)
+		public virtual S? VisitAssignmentExpression(AssignmentExpression assignmentExpression, T data)
 		{
 			return VisitChildren(assignmentExpression, data);
 		}
 
-		public virtual S VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression, T data)
+		public virtual S? VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression, T data)
 		{
 			return VisitChildren(baseReferenceExpression, data);
 		}
 
-		public virtual S VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression, T data)
+		public virtual S? VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression, T data)
 		{
 			return VisitChildren(binaryOperatorExpression, data);
 		}
 
-		public virtual S VisitCastExpression(CastExpression castExpression, T data)
+		public virtual S? VisitCastExpression(CastExpression castExpression, T data)
 		{
 			return VisitChildren(castExpression, data);
 		}
 
-		public virtual S VisitCheckedExpression(CheckedExpression checkedExpression, T data)
+		public virtual S? VisitCheckedExpression(CheckedExpression checkedExpression, T data)
 		{
 			return VisitChildren(checkedExpression, data);
 		}
 
-		public virtual S VisitConditionalExpression(ConditionalExpression conditionalExpression, T data)
+		public virtual S? VisitConditionalExpression(ConditionalExpression conditionalExpression, T data)
 		{
 			return VisitChildren(conditionalExpression, data);
 		}
 
-		public virtual S VisitIdentifierExpression(IdentifierExpression identifierExpression, T data)
+		public virtual S? VisitIdentifierExpression(IdentifierExpression identifierExpression, T data)
 		{
 			return VisitChildren(identifierExpression, data);
 		}
 
-		public virtual S VisitIndexerExpression(IndexerExpression indexerExpression, T data)
+		public virtual S? VisitIndexerExpression(IndexerExpression indexerExpression, T data)
 		{
 			return VisitChildren(indexerExpression, data);
 		}
 
-		public virtual S VisitInterpolatedStringExpression(InterpolatedStringExpression interpolatedStringExpression, T data)
+		public virtual S? VisitInterpolatedStringExpression(InterpolatedStringExpression interpolatedStringExpression, T data)
 		{
 			return VisitChildren(interpolatedStringExpression, data);
 		}
 
-		public virtual S VisitInterpolation(Interpolation interpolation, T data)
+		public virtual S? VisitInterpolation(Interpolation interpolation, T data)
 		{
 			return VisitChildren(interpolation, data);
 		}
 
-		public virtual S VisitInterpolatedStringText(InterpolatedStringText interpolatedStringText, T data)
+		public virtual S? VisitInterpolatedStringText(InterpolatedStringText interpolatedStringText, T data)
 		{
 			return VisitChildren(interpolatedStringText, data);
 		}
 
-		public virtual S VisitInvocationExpression(InvocationExpression invocationExpression, T data)
+		public virtual S? VisitInvocationExpression(InvocationExpression invocationExpression, T data)
 		{
 			return VisitChildren(invocationExpression, data);
 		}
 
-		public virtual S VisitDirectionExpression(DirectionExpression directionExpression, T data)
+		public virtual S? VisitDirectionExpression(DirectionExpression directionExpression, T data)
 		{
 			return VisitChildren(directionExpression, data);
 		}
 
-		public virtual S VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression, T data)
+		public virtual S? VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression, T data)
 		{
 			return VisitChildren(memberReferenceExpression, data);
 		}
 
-		public virtual S VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression, T data)
+		public virtual S? VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression, T data)
 		{
 			return VisitChildren(nullReferenceExpression, data);
 		}
 
-		public virtual S VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression, T data)
+		public virtual S? VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression, T data)
 		{
 			return VisitChildren(objectCreateExpression, data);
 		}
 
-		public virtual S VisitDeclarationExpression(DeclarationExpression declarationExpression, T data)
+		public virtual S? VisitDeclarationExpression(DeclarationExpression declarationExpression, T data)
 		{
 			return VisitChildren(declarationExpression, data);
 		}
 
-		public virtual S VisitRecursivePatternExpression(RecursivePatternExpression recursivePatternExpression, T data)
+		public virtual S? VisitRecursivePatternExpression(RecursivePatternExpression recursivePatternExpression, T data)
 		{
 			return VisitChildren(recursivePatternExpression, data);
 		}
 
-		public virtual S VisitOutVarDeclarationExpression(OutVarDeclarationExpression outVarDeclarationExpression, T data)
+		public virtual S? VisitOutVarDeclarationExpression(OutVarDeclarationExpression outVarDeclarationExpression, T data)
 		{
 			return VisitChildren(outVarDeclarationExpression, data);
 		}
 
-		public virtual S VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression, T data)
+		public virtual S? VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression, T data)
 		{
 			return VisitChildren(anonymousTypeCreateExpression, data);
 		}
 
-		public virtual S VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression, T data)
+		public virtual S? VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression, T data)
 		{
 			return VisitChildren(arrayCreateExpression, data);
 		}
 
-		public virtual S VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression, T data)
+		public virtual S? VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression, T data)
 		{
 			return VisitChildren(parenthesizedExpression, data);
 		}
 
-		public virtual S VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression, T data)
+		public virtual S? VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression, T data)
 		{
 			return VisitChildren(pointerReferenceExpression, data);
 		}
 
-		public virtual S VisitPrimitiveExpression(PrimitiveExpression primitiveExpression, T data)
+		public virtual S? VisitPrimitiveExpression(PrimitiveExpression primitiveExpression, T data)
 		{
 			return VisitChildren(primitiveExpression, data);
 		}
 
-		public virtual S VisitSizeOfExpression(SizeOfExpression sizeOfExpression, T data)
+		public virtual S? VisitSizeOfExpression(SizeOfExpression sizeOfExpression, T data)
 		{
 			return VisitChildren(sizeOfExpression, data);
 		}
 
-		public virtual S VisitStackAllocExpression(StackAllocExpression stackAllocExpression, T data)
+		public virtual S? VisitStackAllocExpression(StackAllocExpression stackAllocExpression, T data)
 		{
 			return VisitChildren(stackAllocExpression, data);
 		}
 
-		public virtual S VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression, T data)
+		public virtual S? VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression, T data)
 		{
 			return VisitChildren(thisReferenceExpression, data);
 		}
 
-		public virtual S VisitThrowExpression(ThrowExpression throwExpression, T data)
+		public virtual S? VisitThrowExpression(ThrowExpression throwExpression, T data)
 		{
 			return VisitChildren(throwExpression, data);
 		}
 
-		public virtual S VisitTupleExpression(TupleExpression tupleExpression, T data)
+		public virtual S? VisitTupleExpression(TupleExpression tupleExpression, T data)
 		{
 			return VisitChildren(tupleExpression, data);
 		}
 
-		public virtual S VisitTypeOfExpression(TypeOfExpression typeOfExpression, T data)
+		public virtual S? VisitTypeOfExpression(TypeOfExpression typeOfExpression, T data)
 		{
 			return VisitChildren(typeOfExpression, data);
 		}
 
-		public virtual S VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression, T data)
+		public virtual S? VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression, T data)
 		{
 			return VisitChildren(typeReferenceExpression, data);
 		}
 
-		public virtual S VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression, T data)
+		public virtual S? VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression, T data)
 		{
 			return VisitChildren(unaryOperatorExpression, data);
 		}
 
-		public virtual S VisitUncheckedExpression(UncheckedExpression uncheckedExpression, T data)
+		public virtual S? VisitUncheckedExpression(UncheckedExpression uncheckedExpression, T data)
 		{
 			return VisitChildren(uncheckedExpression, data);
 		}
 
-		public virtual S VisitQueryExpression(QueryExpression queryExpression, T data)
+		public virtual S? VisitQueryExpression(QueryExpression queryExpression, T data)
 		{
 			return VisitChildren(queryExpression, data);
 		}
 
-		public virtual S VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause, T data)
+		public virtual S? VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause, T data)
 		{
 			return VisitChildren(queryContinuationClause, data);
 		}
 
-		public virtual S VisitQueryFromClause(QueryFromClause queryFromClause, T data)
+		public virtual S? VisitQueryFromClause(QueryFromClause queryFromClause, T data)
 		{
 			return VisitChildren(queryFromClause, data);
 		}
 
-		public virtual S VisitQueryLetClause(QueryLetClause queryLetClause, T data)
+		public virtual S? VisitQueryLetClause(QueryLetClause queryLetClause, T data)
 		{
 			return VisitChildren(queryLetClause, data);
 		}
 
-		public virtual S VisitQueryWhereClause(QueryWhereClause queryWhereClause, T data)
+		public virtual S? VisitQueryWhereClause(QueryWhereClause queryWhereClause, T data)
 		{
 			return VisitChildren(queryWhereClause, data);
 		}
 
-		public virtual S VisitQueryJoinClause(QueryJoinClause queryJoinClause, T data)
+		public virtual S? VisitQueryJoinClause(QueryJoinClause queryJoinClause, T data)
 		{
 			return VisitChildren(queryJoinClause, data);
 		}
 
-		public virtual S VisitQueryOrderClause(QueryOrderClause queryOrderClause, T data)
+		public virtual S? VisitQueryOrderClause(QueryOrderClause queryOrderClause, T data)
 		{
 			return VisitChildren(queryOrderClause, data);
 		}
 
-		public virtual S VisitQueryOrdering(QueryOrdering queryOrdering, T data)
+		public virtual S? VisitQueryOrdering(QueryOrdering queryOrdering, T data)
 		{
 			return VisitChildren(queryOrdering, data);
 		}
 
-		public virtual S VisitQuerySelectClause(QuerySelectClause querySelectClause, T data)
+		public virtual S? VisitQuerySelectClause(QuerySelectClause querySelectClause, T data)
 		{
 			return VisitChildren(querySelectClause, data);
 		}
 
-		public virtual S VisitQueryGroupClause(QueryGroupClause queryGroupClause, T data)
+		public virtual S? VisitQueryGroupClause(QueryGroupClause queryGroupClause, T data)
 		{
 			return VisitChildren(queryGroupClause, data);
 		}
 
-		public virtual S VisitAsExpression(AsExpression asExpression, T data)
+		public virtual S? VisitAsExpression(AsExpression asExpression, T data)
 		{
 			return VisitChildren(asExpression, data);
 		}
 
-		public virtual S VisitIsExpression(IsExpression isExpression, T data)
+		public virtual S? VisitIsExpression(IsExpression isExpression, T data)
 		{
 			return VisitChildren(isExpression, data);
 		}
 
-		public virtual S VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression, T data)
+		public virtual S? VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression, T data)
 		{
 			return VisitChildren(defaultValueExpression, data);
 		}
 
-		public virtual S VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression, T data)
+		public virtual S? VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression, T data)
 		{
 			return VisitChildren(undocumentedExpression, data);
 		}
 
-		public virtual S VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression, T data)
+		public virtual S? VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression, T data)
 		{
 			return VisitChildren(arrayInitializerExpression, data);
 		}
 
-		public virtual S VisitArraySpecifier(ArraySpecifier arraySpecifier, T data)
+		public virtual S? VisitArraySpecifier(ArraySpecifier arraySpecifier, T data)
 		{
 			return VisitChildren(arraySpecifier, data);
 		}
 
-		public virtual S VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression, T data)
+		public virtual S? VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression, T data)
 		{
 			return VisitChildren(namedArgumentExpression, data);
 		}
 
-		public virtual S VisitNamedExpression(NamedExpression namedExpression, T data)
+		public virtual S? VisitNamedExpression(NamedExpression namedExpression, T data)
 		{
 			return VisitChildren(namedExpression, data);
 		}
 
-		public virtual S VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation, T data)
+		public virtual S? VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation, T data)
 		{
 			return VisitChildren(singleVariableDesignation, data);
 		}
 
-		public virtual S VisitParenthesizedVariableDesignation(ParenthesizedVariableDesignation parenthesizedVariableDesignation, T data)
+		public virtual S? VisitParenthesizedVariableDesignation(ParenthesizedVariableDesignation parenthesizedVariableDesignation, T data)
 		{
 			return VisitChildren(parenthesizedVariableDesignation, data);
 		}
 
-		public virtual S VisitErrorNode(AstNode errorNode, T data)
+		public virtual S? VisitErrorNode(AstNode errorNode, T data)
 		{
 			return VisitChildren(errorNode, data);
 		}
 
-		public virtual S VisitPatternPlaceholder(AstNode placeholder, PatternMatching.Pattern pattern, T data)
+		public virtual S? VisitPatternPlaceholder(AstNode placeholder, PatternMatching.Pattern pattern, T data)
 		{
 			return VisitChildren(placeholder, data);
 		}
 
-		public virtual S VisitWithInitializerExpression(WithInitializerExpression withInitializerExpression, T data)
+		public virtual S? VisitWithInitializerExpression(WithInitializerExpression withInitializerExpression, T data)
 		{
 			return VisitChildren(withInitializerExpression, data);
 		}

ICSharpCode.Decompiler/CSharp/Syntax/IAnnotatable.cs

@@ -42,7 +42,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// <typeparam name='T'>
 		/// The type of the annotation.
 		/// </typeparam>
-		T Annotation<T>() where T : class;
+		T? Annotation<T>() where T : class;
 
 		/// <summary>
 		/// Gets the first annotation of the specified type.
@@ -51,7 +51,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// <param name='type'>
 		/// The type of the annotation.
 		/// </param>
-		object Annotation(Type type);
+		object? Annotation(Type type);
 
 		/// <summary>
 		/// Adds an annotation to this instance.
@@ -89,7 +89,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		// or to an AnnotationList.
 		// Once it is pointed at an AnnotationList, it will never change (this allows thread-safety support by locking the list)
 
-		object annotations;
+		object? annotations;
 
 		/// <summary>
 		/// Clones all annotations.
@@ -136,7 +136,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			if (annotation == null)
 				throw new ArgumentNullException(nameof(annotation));
 			retry: // Retry until successful
-			object oldAnnotation = Interlocked.CompareExchange(ref this.annotations, annotation, null);
+			object? oldAnnotation = Interlocked.CompareExchange(ref this.annotations, annotation, null);
 			if (oldAnnotation == null)
 			{
 				return; // we successfully added a single annotation
@@ -167,7 +167,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public virtual void RemoveAnnotations<T>() where T : class
 		{
 			retry: // Retry until successful
-			object oldAnnotations = this.annotations;
+			object? oldAnnotations = this.annotations;
 			AnnotationList? list = oldAnnotations as AnnotationList;
 			if (list != null)
 			{
@@ -189,7 +189,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			if (type == null)
 				throw new ArgumentNullException(nameof(type));
 			retry: // Retry until successful
-			object oldAnnotations = this.annotations;
+			object? oldAnnotations = this.annotations;
 			AnnotationList? list = oldAnnotations as AnnotationList;
 			if (list != null)
 			{
@@ -206,9 +206,9 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			}
 		}
 
-		public T Annotation<T>() where T : class
+		public T? Annotation<T>() where T : class
 		{
-			object annotations = this.annotations;
+			object? annotations = this.annotations;
 			AnnotationList? list = annotations as AnnotationList;
 			if (list != null)
 			{
@@ -229,11 +229,11 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			}
 		}
 
-		public object Annotation(Type type)
+		public object? Annotation(Type type)
 		{
 			if (type == null)
 				throw new ArgumentNullException(nameof(type));
-			object annotations = this.annotations;
+			object? annotations = this.annotations;
 			AnnotationList? list = annotations as AnnotationList;
 			if (list != null)
 			{
@@ -259,7 +259,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// </summary>
 		public IEnumerable<object> Annotations {
 			get {
-				object annotations = this.annotations;
+				object? annotations = this.annotations;
 				AnnotationList? list = annotations as AnnotationList;
 				if (list != null)
 				{

ICSharpCode.Decompiler/CSharp/Syntax/IAstVisitor.cs

@@ -173,148 +173,148 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	/// </summary>
 	public interface IAstVisitor<out S>
 	{
-		S VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression);
-		S VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression);
-		S VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression);
-		S VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression);
-		S VisitAsExpression(AsExpression asExpression);
-		S VisitAssignmentExpression(AssignmentExpression assignmentExpression);
-		S VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression);
-		S VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression);
-		S VisitCastExpression(CastExpression castExpression);
-		S VisitCheckedExpression(CheckedExpression checkedExpression);
-		S VisitConditionalExpression(ConditionalExpression conditionalExpression);
-		S VisitDeclarationExpression(DeclarationExpression declarationExpression);
-		S VisitRecursivePatternExpression(RecursivePatternExpression recursivePatternExpression);
-		S VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression);
-		S VisitDirectionExpression(DirectionExpression directionExpression);
-		S VisitIdentifierExpression(IdentifierExpression identifierExpression);
-		S VisitIndexerExpression(IndexerExpression indexerExpression);
-		S VisitInterpolatedStringExpression(InterpolatedStringExpression interpolatedStringExpression);
-		S VisitInvocationExpression(InvocationExpression invocationExpression);
-		S VisitIsExpression(IsExpression isExpression);
-		S VisitLambdaExpression(LambdaExpression lambdaExpression);
-		S VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression);
-		S VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression);
-		S VisitNamedExpression(NamedExpression namedExpression);
-		S VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression);
-		S VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression);
-		S VisitOutVarDeclarationExpression(OutVarDeclarationExpression outVarDeclarationExpression);
-		S VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression);
-		S VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression);
-		S VisitPrimitiveExpression(PrimitiveExpression primitiveExpression);
-		S VisitSizeOfExpression(SizeOfExpression sizeOfExpression);
-		S VisitStackAllocExpression(StackAllocExpression stackAllocExpression);
-		S VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression);
-		S VisitThrowExpression(ThrowExpression throwExpression);
-		S VisitTupleExpression(TupleExpression tupleExpression);
-		S VisitTypeOfExpression(TypeOfExpression typeOfExpression);
-		S VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression);
-		S VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression);
-		S VisitUncheckedExpression(UncheckedExpression uncheckedExpression);
-		S VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression);
-		S VisitWithInitializerExpression(WithInitializerExpression withInitializerExpression);
-
-		S VisitQueryExpression(QueryExpression queryExpression);
-		S VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause);
-		S VisitQueryFromClause(QueryFromClause queryFromClause);
-		S VisitQueryLetClause(QueryLetClause queryLetClause);
-		S VisitQueryWhereClause(QueryWhereClause queryWhereClause);
-		S VisitQueryJoinClause(QueryJoinClause queryJoinClause);
-		S VisitQueryOrderClause(QueryOrderClause queryOrderClause);
-		S VisitQueryOrdering(QueryOrdering queryOrdering);
-		S VisitQuerySelectClause(QuerySelectClause querySelectClause);
-		S VisitQueryGroupClause(QueryGroupClause queryGroupClause);
-
-		S VisitAttribute(Attribute attribute);
-		S VisitAttributeSection(AttributeSection attributeSection);
-		S VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration);
-		S VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration);
-		S VisitTypeDeclaration(TypeDeclaration typeDeclaration);
-		S VisitUsingAliasDeclaration(UsingAliasDeclaration usingAliasDeclaration);
-		S VisitUsingDeclaration(UsingDeclaration usingDeclaration);
-		S VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration);
-
-		S VisitBlockStatement(BlockStatement blockStatement);
-		S VisitBreakStatement(BreakStatement breakStatement);
-		S VisitCheckedStatement(CheckedStatement checkedStatement);
-		S VisitContinueStatement(ContinueStatement continueStatement);
-		S VisitDoWhileStatement(DoWhileStatement doWhileStatement);
-		S VisitEmptyStatement(EmptyStatement emptyStatement);
-		S VisitExpressionStatement(ExpressionStatement expressionStatement);
-		S VisitFixedStatement(FixedStatement fixedStatement);
-		S VisitForeachStatement(ForeachStatement foreachStatement);
-		S VisitForStatement(ForStatement forStatement);
-		S VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement);
-		S VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement);
-		S VisitGotoStatement(GotoStatement gotoStatement);
-		S VisitIfElseStatement(IfElseStatement ifElseStatement);
-		S VisitLabelStatement(LabelStatement labelStatement);
-		S VisitLockStatement(LockStatement lockStatement);
-		S VisitReturnStatement(ReturnStatement returnStatement);
-		S VisitSwitchStatement(SwitchStatement switchStatement);
-		S VisitSwitchSection(SwitchSection switchSection);
-		S VisitCaseLabel(CaseLabel caseLabel);
-		S VisitSwitchExpression(SwitchExpression switchExpression);
-		S VisitSwitchExpressionSection(SwitchExpressionSection switchExpressionSection);
-		S VisitThrowStatement(ThrowStatement throwStatement);
-		S VisitTryCatchStatement(TryCatchStatement tryCatchStatement);
-		S VisitCatchClause(CatchClause catchClause);
-		S VisitUncheckedStatement(UncheckedStatement uncheckedStatement);
-		S VisitUnsafeStatement(UnsafeStatement unsafeStatement);
-		S VisitUsingStatement(UsingStatement usingStatement);
-		S VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement);
-		S VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement);
-		S VisitWhileStatement(WhileStatement whileStatement);
-		S VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement);
-		S VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement);
-
-		S VisitAccessor(Accessor accessor);
-		S VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration);
-		S VisitConstructorInitializer(ConstructorInitializer constructorInitializer);
-		S VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration);
-		S VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration);
-		S VisitEventDeclaration(EventDeclaration eventDeclaration);
-		S VisitCustomEventDeclaration(CustomEventDeclaration customEventDeclaration);
-		S VisitFieldDeclaration(FieldDeclaration fieldDeclaration);
-		S VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration);
-		S VisitMethodDeclaration(MethodDeclaration methodDeclaration);
-		S VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration);
-		S VisitParameterDeclaration(ParameterDeclaration parameterDeclaration);
-		S VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration);
-		S VisitVariableInitializer(VariableInitializer variableInitializer);
-		S VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration);
-		S VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer);
-
-		S VisitSyntaxTree(SyntaxTree syntaxTree);
-		S VisitSimpleType(SimpleType simpleType);
-		S VisitMemberType(MemberType memberType);
-		S VisitTupleType(TupleAstType tupleType);
-		S VisitTupleTypeElement(TupleTypeElement tupleTypeElement);
-		S VisitFunctionPointerType(FunctionPointerAstType functionPointerType);
-		S VisitInvocationType(InvocationAstType invocationType);
-		S VisitComposedType(ComposedType composedType);
-		S VisitArraySpecifier(ArraySpecifier arraySpecifier);
-		S VisitPrimitiveType(PrimitiveType primitiveType);
-
-		S VisitComment(Comment comment);
-		S VisitPreProcessorDirective(PreProcessorDirective preProcessorDirective);
-		S VisitDocumentationReference(DocumentationReference documentationReference);
-
-		S VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration);
-		S VisitConstraint(Constraint constraint);
-		S VisitCSharpTokenNode(CSharpTokenNode cSharpTokenNode);
-		S VisitIdentifier(Identifier identifier);
-
-		S VisitInterpolation(Interpolation interpolation);
-		S VisitInterpolatedStringText(InterpolatedStringText interpolatedStringText);
-
-		S VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation);
-		S VisitParenthesizedVariableDesignation(ParenthesizedVariableDesignation parenthesizedVariableDesignation);
-
-		S VisitNullNode(AstNode nullNode);
-		S VisitErrorNode(AstNode errorNode);
-		S VisitPatternPlaceholder(AstNode placeholder, PatternMatching.Pattern pattern);
+		S? VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression);
+		S? VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression);
+		S? VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression);
+		S? VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression);
+		S? VisitAsExpression(AsExpression asExpression);
+		S? VisitAssignmentExpression(AssignmentExpression assignmentExpression);
+		S? VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression);
+		S? VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression);
+		S? VisitCastExpression(CastExpression castExpression);
+		S? VisitCheckedExpression(CheckedExpression checkedExpression);
+		S? VisitConditionalExpression(ConditionalExpression conditionalExpression);
+		S? VisitDeclarationExpression(DeclarationExpression declarationExpression);
+		S? VisitRecursivePatternExpression(RecursivePatternExpression recursivePatternExpression);
+		S? VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression);
+		S? VisitDirectionExpression(DirectionExpression directionExpression);
+		S? VisitIdentifierExpression(IdentifierExpression identifierExpression);
+		S? VisitIndexerExpression(IndexerExpression indexerExpression);
+		S? VisitInterpolatedStringExpression(InterpolatedStringExpression interpolatedStringExpression);
+		S? VisitInvocationExpression(InvocationExpression invocationExpression);
+		S? VisitIsExpression(IsExpression isExpression);
+		S? VisitLambdaExpression(LambdaExpression lambdaExpression);
+		S? VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression);
+		S? VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression);
+		S? VisitNamedExpression(NamedExpression namedExpression);
+		S? VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression);
+		S? VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression);
+		S? VisitOutVarDeclarationExpression(OutVarDeclarationExpression outVarDeclarationExpression);
+		S? VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression);
+		S? VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression);
+		S? VisitPrimitiveExpression(PrimitiveExpression primitiveExpression);
+		S? VisitSizeOfExpression(SizeOfExpression sizeOfExpression);
+		S? VisitStackAllocExpression(StackAllocExpression stackAllocExpression);
+		S? VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression);
+		S? VisitThrowExpression(ThrowExpression throwExpression);
+		S? VisitTupleExpression(TupleExpression tupleExpression);
+		S? VisitTypeOfExpression(TypeOfExpression typeOfExpression);
+		S? VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression);
+		S? VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression);
+		S? VisitUncheckedExpression(UncheckedExpression uncheckedExpression);
+		S? VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression);
+		S? VisitWithInitializerExpression(WithInitializerExpression withInitializerExpression);
+
+		S? VisitQueryExpression(QueryExpression queryExpression);
+		S? VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause);
+		S? VisitQueryFromClause(QueryFromClause queryFromClause);
+		S? VisitQueryLetClause(QueryLetClause queryLetClause);
+		S? VisitQueryWhereClause(QueryWhereClause queryWhereClause);
+		S? VisitQueryJoinClause(QueryJoinClause queryJoinClause);
+		S? VisitQueryOrderClause(QueryOrderClause queryOrderClause);
+		S? VisitQueryOrdering(QueryOrdering queryOrdering);
+		S? VisitQuerySelectClause(QuerySelectClause querySelectClause);
+		S? VisitQueryGroupClause(QueryGroupClause queryGroupClause);
+
+		S? VisitAttribute(Attribute attribute);
+		S? VisitAttributeSection(AttributeSection attributeSection);
+		S? VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration);
+		S? VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration);
+		S? VisitTypeDeclaration(TypeDeclaration typeDeclaration);
+		S? VisitUsingAliasDeclaration(UsingAliasDeclaration usingAliasDeclaration);
+		S? VisitUsingDeclaration(UsingDeclaration usingDeclaration);
+		S? VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration);
+
+		S? VisitBlockStatement(BlockStatement blockStatement);
+		S? VisitBreakStatement(BreakStatement breakStatement);
+		S? VisitCheckedStatement(CheckedStatement checkedStatement);
+		S? VisitContinueStatement(ContinueStatement continueStatement);
+		S? VisitDoWhileStatement(DoWhileStatement doWhileStatement);
+		S? VisitEmptyStatement(EmptyStatement emptyStatement);
+		S? VisitExpressionStatement(ExpressionStatement expressionStatement);
+		S? VisitFixedStatement(FixedStatement fixedStatement);
+		S? VisitForeachStatement(ForeachStatement foreachStatement);
+		S? VisitForStatement(ForStatement forStatement);
+		S? VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement);
+		S? VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement);
+		S? VisitGotoStatement(GotoStatement gotoStatement);
+		S? VisitIfElseStatement(IfElseStatement ifElseStatement);
+		S? VisitLabelStatement(LabelStatement labelStatement);
+		S? VisitLockStatement(LockStatement lockStatement);
+		S? VisitReturnStatement(ReturnStatement returnStatement);
+		S? VisitSwitchStatement(SwitchStatement switchStatement);
+		S? VisitSwitchSection(SwitchSection switchSection);
+		S? VisitCaseLabel(CaseLabel caseLabel);
+		S? VisitSwitchExpression(SwitchExpression switchExpression);
+		S? VisitSwitchExpressionSection(SwitchExpressionSection switchExpressionSection);
+		S? VisitThrowStatement(ThrowStatement throwStatement);
+		S? VisitTryCatchStatement(TryCatchStatement tryCatchStatement);
+		S? VisitCatchClause(CatchClause catchClause);
+		S? VisitUncheckedStatement(UncheckedStatement uncheckedStatement);
+		S? VisitUnsafeStatement(UnsafeStatement unsafeStatement);
+		S? VisitUsingStatement(UsingStatement usingStatement);
+		S? VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement);
+		S? VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement);
+		S? VisitWhileStatement(WhileStatement whileStatement);
+		S? VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement);
+		S? VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement);
+
+		S? VisitAccessor(Accessor accessor);
+		S? VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration);
+		S? VisitConstructorInitializer(ConstructorInitializer constructorInitializer);
+		S? VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration);
+		S? VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration);
+		S? VisitEventDeclaration(EventDeclaration eventDeclaration);
+		S? VisitCustomEventDeclaration(CustomEventDeclaration customEventDeclaration);
+		S? VisitFieldDeclaration(FieldDeclaration fieldDeclaration);
+		S? VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration);
+		S? VisitMethodDeclaration(MethodDeclaration methodDeclaration);
+		S? VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration);
+		S? VisitParameterDeclaration(ParameterDeclaration parameterDeclaration);
+		S? VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration);
+		S? VisitVariableInitializer(VariableInitializer variableInitializer);
+		S? VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration);
+		S? VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer);
+
+		S? VisitSyntaxTree(SyntaxTree syntaxTree);
+		S? VisitSimpleType(SimpleType simpleType);
+		S? VisitMemberType(MemberType memberType);
+		S? VisitTupleType(TupleAstType tupleType);
+		S? VisitTupleTypeElement(TupleTypeElement tupleTypeElement);
+		S? VisitFunctionPointerType(FunctionPointerAstType functionPointerType);
+		S? VisitInvocationType(InvocationAstType invocationType);
+		S? VisitComposedType(ComposedType composedType);
+		S? VisitArraySpecifier(ArraySpecifier arraySpecifier);
+		S? VisitPrimitiveType(PrimitiveType primitiveType);
+
+		S? VisitComment(Comment comment);
+		S? VisitPreProcessorDirective(PreProcessorDirective preProcessorDirective);
+		S? VisitDocumentationReference(DocumentationReference documentationReference);
+
+		S? VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration);
+		S? VisitConstraint(Constraint constraint);
+		S? VisitCSharpTokenNode(CSharpTokenNode cSharpTokenNode);
+		S? VisitIdentifier(Identifier identifier);
+
+		S? VisitInterpolation(Interpolation interpolation);
+		S? VisitInterpolatedStringText(InterpolatedStringText interpolatedStringText);
+
+		S? VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation);
+		S? VisitParenthesizedVariableDesignation(ParenthesizedVariableDesignation parenthesizedVariableDesignation);
+
+		S? VisitNullNode(AstNode nullNode);
+		S? VisitErrorNode(AstNode errorNode);
+		S? VisitPatternPlaceholder(AstNode placeholder, PatternMatching.Pattern pattern);
 	}
 
 	/// <summary>
@@ -322,147 +322,147 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	/// </summary>
 	public interface IAstVisitor<in T, out S>
 	{
-		S VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression, T data);
-		S VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression, T data);
-		S VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression, T data);
-		S VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression, T data);
-		S VisitAsExpression(AsExpression asExpression, T data);
-		S VisitAssignmentExpression(AssignmentExpression assignmentExpression, T data);
-		S VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression, T data);
-		S VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression, T data);
-		S VisitCastExpression(CastExpression castExpression, T data);
-		S VisitCheckedExpression(CheckedExpression checkedExpression, T data);
-		S VisitConditionalExpression(ConditionalExpression conditionalExpression, T data);
-		S VisitDeclarationExpression(DeclarationExpression declarationExpression, T data);
-		S VisitRecursivePatternExpression(RecursivePatternExpression recursivePatternExpression, T data);
-		S VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression, T data);
-		S VisitDirectionExpression(DirectionExpression directionExpression, T data);
-		S VisitIdentifierExpression(IdentifierExpression identifierExpression, T data);
-		S VisitIndexerExpression(IndexerExpression indexerExpression, T data);
-		S VisitInterpolatedStringExpression(InterpolatedStringExpression interpolatedStringExpression, T data);
-		S VisitInvocationExpression(InvocationExpression invocationExpression, T data);
-		S VisitIsExpression(IsExpression isExpression, T data);
-		S VisitLambdaExpression(LambdaExpression lambdaExpression, T data);
-		S VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression, T data);
-		S VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression, T data);
-		S VisitNamedExpression(NamedExpression namedExpression, T data);
-		S VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression, T data);
-		S VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression, T data);
-		S VisitOutVarDeclarationExpression(OutVarDeclarationExpression outVarDeclarationExpression, T data);
-		S VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression, T data);
-		S VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression, T data);
-		S VisitPrimitiveExpression(PrimitiveExpression primitiveExpression, T data);
-		S VisitSizeOfExpression(SizeOfExpression sizeOfExpression, T data);
-		S VisitStackAllocExpression(StackAllocExpression stackAllocExpression, T data);
-		S VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression, T data);
-		S VisitThrowExpression(ThrowExpression throwExpression, T data);
-		S VisitTupleExpression(TupleExpression tupleExpression, T data);
-		S VisitTypeOfExpression(TypeOfExpression typeOfExpression, T data);
-		S VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression, T data);
-		S VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression, T data);
-		S VisitUncheckedExpression(UncheckedExpression uncheckedExpression, T data);
-		S VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression, T data);
-		S VisitWithInitializerExpression(WithInitializerExpression withInitializerExpression, T data);
-
-		S VisitQueryExpression(QueryExpression queryExpression, T data);
-		S VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause, T data);
-		S VisitQueryFromClause(QueryFromClause queryFromClause, T data);
-		S VisitQueryLetClause(QueryLetClause queryLetClause, T data);
-		S VisitQueryWhereClause(QueryWhereClause queryWhereClause, T data);
-		S VisitQueryJoinClause(QueryJoinClause queryJoinClause, T data);
-		S VisitQueryOrderClause(QueryOrderClause queryOrderClause, T data);
-		S VisitQueryOrdering(QueryOrdering queryOrdering, T data);
-		S VisitQuerySelectClause(QuerySelectClause querySelectClause, T data);
-		S VisitQueryGroupClause(QueryGroupClause queryGroupClause, T data);
-
-		S VisitAttribute(Attribute attribute, T data);
-		S VisitAttributeSection(AttributeSection attributeSection, T data);
-		S VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration, T data);
-		S VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration, T data);
-		S VisitTypeDeclaration(TypeDeclaration typeDeclaration, T data);
-		S VisitUsingAliasDeclaration(UsingAliasDeclaration usingAliasDeclaration, T data);
-		S VisitUsingDeclaration(UsingDeclaration usingDeclaration, T data);
-		S VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration, T data);
-
-		S VisitBlockStatement(BlockStatement blockStatement, T data);
-		S VisitBreakStatement(BreakStatement breakStatement, T data);
-		S VisitCheckedStatement(CheckedStatement checkedStatement, T data);
-		S VisitContinueStatement(ContinueStatement continueStatement, T data);
-		S VisitDoWhileStatement(DoWhileStatement doWhileStatement, T data);
-		S VisitEmptyStatement(EmptyStatement emptyStatement, T data);
-		S VisitExpressionStatement(ExpressionStatement expressionStatement, T data);
-		S VisitFixedStatement(FixedStatement fixedStatement, T data);
-		S VisitForeachStatement(ForeachStatement foreachStatement, T data);
-		S VisitForStatement(ForStatement forStatement, T data);
-		S VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement, T data);
-		S VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement, T data);
-		S VisitGotoStatement(GotoStatement gotoStatement, T data);
-		S VisitIfElseStatement(IfElseStatement ifElseStatement, T data);
-		S VisitLabelStatement(LabelStatement labelStatement, T data);
-		S VisitLockStatement(LockStatement lockStatement, T data);
-		S VisitReturnStatement(ReturnStatement returnStatement, T data);
-		S VisitSwitchStatement(SwitchStatement switchStatement, T data);
-		S VisitSwitchSection(SwitchSection switchSection, T data);
-		S VisitCaseLabel(CaseLabel caseLabel, T data);
-		S VisitSwitchExpression(SwitchExpression switchExpression, T data);
-		S VisitSwitchExpressionSection(SwitchExpressionSection switchExpressionSection, T data);
-		S VisitThrowStatement(ThrowStatement throwStatement, T data);
-		S VisitTryCatchStatement(TryCatchStatement tryCatchStatement, T data);
-		S VisitCatchClause(CatchClause catchClause, T data);
-		S VisitUncheckedStatement(UncheckedStatement uncheckedStatement, T data);
-		S VisitUnsafeStatement(UnsafeStatement unsafeStatement, T data);
-		S VisitUsingStatement(UsingStatement usingStatement, T data);
-		S VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement, T data);
-		S VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement, T data);
-		S VisitWhileStatement(WhileStatement whileStatement, T data);
-		S VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement, T data);
-		S VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement, T data);
-
-		S VisitAccessor(Accessor accessor, T data);
-		S VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration, T data);
-		S VisitConstructorInitializer(ConstructorInitializer constructorInitializer, T data);
-		S VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration, T data);
-		S VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration, T data);
-		S VisitEventDeclaration(EventDeclaration eventDeclaration, T data);
-		S VisitCustomEventDeclaration(CustomEventDeclaration customEventDeclaration, T data);
-		S VisitFieldDeclaration(FieldDeclaration fieldDeclaration, T data);
-		S VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration, T data);
-		S VisitMethodDeclaration(MethodDeclaration methodDeclaration, T data);
-		S VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration, T data);
-		S VisitParameterDeclaration(ParameterDeclaration parameterDeclaration, T data);
-		S VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration, T data);
-		S VisitVariableInitializer(VariableInitializer variableInitializer, T data);
-		S VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration, T data);
-		S VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer, T data);
-
-		S VisitSyntaxTree(SyntaxTree syntaxTree, T data);
-		S VisitSimpleType(SimpleType simpleType, T data);
-		S VisitMemberType(MemberType memberType, T data);
-		S VisitTupleType(TupleAstType tupleType, T data);
-		S VisitTupleTypeElement(TupleTypeElement tupleTypeElement, T data);
-		S VisitFunctionPointerType(FunctionPointerAstType functionPointerType, T data);
-		S VisitInvocationType(InvocationAstType invocationType, T data);
-		S VisitComposedType(ComposedType composedType, T data);
-		S VisitArraySpecifier(ArraySpecifier arraySpecifier, T data);
-		S VisitPrimitiveType(PrimitiveType primitiveType, T data);
-
-		S VisitComment(Comment comment, T data);
-		S VisitPreProcessorDirective(PreProcessorDirective preProcessorDirective, T data);
-		S VisitDocumentationReference(DocumentationReference documentationReference, T data);
-
-		S VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration, T data);
-		S VisitConstraint(Constraint constraint, T data);
-		S VisitCSharpTokenNode(CSharpTokenNode cSharpTokenNode, T data);
-		S VisitIdentifier(Identifier identifier, T data);
-
-		S VisitInterpolation(Interpolation interpolation, T data);
-		S VisitInterpolatedStringText(InterpolatedStringText interpolatedStringText, T data);
-
-		S VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation, T data);
-		S VisitParenthesizedVariableDesignation(ParenthesizedVariableDesignation parenthesizedVariableDesignation, T data);
-
-		S VisitNullNode(AstNode nullNode, T data);
-		S VisitErrorNode(AstNode errorNode, T data);
-		S VisitPatternPlaceholder(AstNode placeholder, PatternMatching.Pattern pattern, T data);
+		S? VisitAnonymousMethodExpression(AnonymousMethodExpression anonymousMethodExpression, T data);
+		S? VisitAnonymousTypeCreateExpression(AnonymousTypeCreateExpression anonymousTypeCreateExpression, T data);
+		S? VisitArrayCreateExpression(ArrayCreateExpression arrayCreateExpression, T data);
+		S? VisitArrayInitializerExpression(ArrayInitializerExpression arrayInitializerExpression, T data);
+		S? VisitAsExpression(AsExpression asExpression, T data);
+		S? VisitAssignmentExpression(AssignmentExpression assignmentExpression, T data);
+		S? VisitBaseReferenceExpression(BaseReferenceExpression baseReferenceExpression, T data);
+		S? VisitBinaryOperatorExpression(BinaryOperatorExpression binaryOperatorExpression, T data);
+		S? VisitCastExpression(CastExpression castExpression, T data);
+		S? VisitCheckedExpression(CheckedExpression checkedExpression, T data);
+		S? VisitConditionalExpression(ConditionalExpression conditionalExpression, T data);
+		S? VisitDeclarationExpression(DeclarationExpression declarationExpression, T data);
+		S? VisitRecursivePatternExpression(RecursivePatternExpression recursivePatternExpression, T data);
+		S? VisitDefaultValueExpression(DefaultValueExpression defaultValueExpression, T data);
+		S? VisitDirectionExpression(DirectionExpression directionExpression, T data);
+		S? VisitIdentifierExpression(IdentifierExpression identifierExpression, T data);
+		S? VisitIndexerExpression(IndexerExpression indexerExpression, T data);
+		S? VisitInterpolatedStringExpression(InterpolatedStringExpression interpolatedStringExpression, T data);
+		S? VisitInvocationExpression(InvocationExpression invocationExpression, T data);
+		S? VisitIsExpression(IsExpression isExpression, T data);
+		S? VisitLambdaExpression(LambdaExpression lambdaExpression, T data);
+		S? VisitMemberReferenceExpression(MemberReferenceExpression memberReferenceExpression, T data);
+		S? VisitNamedArgumentExpression(NamedArgumentExpression namedArgumentExpression, T data);
+		S? VisitNamedExpression(NamedExpression namedExpression, T data);
+		S? VisitNullReferenceExpression(NullReferenceExpression nullReferenceExpression, T data);
+		S? VisitObjectCreateExpression(ObjectCreateExpression objectCreateExpression, T data);
+		S? VisitOutVarDeclarationExpression(OutVarDeclarationExpression outVarDeclarationExpression, T data);
+		S? VisitParenthesizedExpression(ParenthesizedExpression parenthesizedExpression, T data);
+		S? VisitPointerReferenceExpression(PointerReferenceExpression pointerReferenceExpression, T data);
+		S? VisitPrimitiveExpression(PrimitiveExpression primitiveExpression, T data);
+		S? VisitSizeOfExpression(SizeOfExpression sizeOfExpression, T data);
+		S? VisitStackAllocExpression(StackAllocExpression stackAllocExpression, T data);
+		S? VisitThisReferenceExpression(ThisReferenceExpression thisReferenceExpression, T data);
+		S? VisitThrowExpression(ThrowExpression throwExpression, T data);
+		S? VisitTupleExpression(TupleExpression tupleExpression, T data);
+		S? VisitTypeOfExpression(TypeOfExpression typeOfExpression, T data);
+		S? VisitTypeReferenceExpression(TypeReferenceExpression typeReferenceExpression, T data);
+		S? VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression, T data);
+		S? VisitUncheckedExpression(UncheckedExpression uncheckedExpression, T data);
+		S? VisitUndocumentedExpression(UndocumentedExpression undocumentedExpression, T data);
+		S? VisitWithInitializerExpression(WithInitializerExpression withInitializerExpression, T data);
+
+		S? VisitQueryExpression(QueryExpression queryExpression, T data);
+		S? VisitQueryContinuationClause(QueryContinuationClause queryContinuationClause, T data);
+		S? VisitQueryFromClause(QueryFromClause queryFromClause, T data);
+		S? VisitQueryLetClause(QueryLetClause queryLetClause, T data);
+		S? VisitQueryWhereClause(QueryWhereClause queryWhereClause, T data);
+		S? VisitQueryJoinClause(QueryJoinClause queryJoinClause, T data);
+		S? VisitQueryOrderClause(QueryOrderClause queryOrderClause, T data);
+		S? VisitQueryOrdering(QueryOrdering queryOrdering, T data);
+		S? VisitQuerySelectClause(QuerySelectClause querySelectClause, T data);
+		S? VisitQueryGroupClause(QueryGroupClause queryGroupClause, T data);
+
+		S? VisitAttribute(Attribute attribute, T data);
+		S? VisitAttributeSection(AttributeSection attributeSection, T data);
+		S? VisitDelegateDeclaration(DelegateDeclaration delegateDeclaration, T data);
+		S? VisitNamespaceDeclaration(NamespaceDeclaration namespaceDeclaration, T data);
+		S? VisitTypeDeclaration(TypeDeclaration typeDeclaration, T data);
+		S? VisitUsingAliasDeclaration(UsingAliasDeclaration usingAliasDeclaration, T data);
+		S? VisitUsingDeclaration(UsingDeclaration usingDeclaration, T data);
+		S? VisitExternAliasDeclaration(ExternAliasDeclaration externAliasDeclaration, T data);
+
+		S? VisitBlockStatement(BlockStatement blockStatement, T data);
+		S? VisitBreakStatement(BreakStatement breakStatement, T data);
+		S? VisitCheckedStatement(CheckedStatement checkedStatement, T data);
+		S? VisitContinueStatement(ContinueStatement continueStatement, T data);
+		S? VisitDoWhileStatement(DoWhileStatement doWhileStatement, T data);
+		S? VisitEmptyStatement(EmptyStatement emptyStatement, T data);
+		S? VisitExpressionStatement(ExpressionStatement expressionStatement, T data);
+		S? VisitFixedStatement(FixedStatement fixedStatement, T data);
+		S? VisitForeachStatement(ForeachStatement foreachStatement, T data);
+		S? VisitForStatement(ForStatement forStatement, T data);
+		S? VisitGotoCaseStatement(GotoCaseStatement gotoCaseStatement, T data);
+		S? VisitGotoDefaultStatement(GotoDefaultStatement gotoDefaultStatement, T data);
+		S? VisitGotoStatement(GotoStatement gotoStatement, T data);
+		S? VisitIfElseStatement(IfElseStatement ifElseStatement, T data);
+		S? VisitLabelStatement(LabelStatement labelStatement, T data);
+		S? VisitLockStatement(LockStatement lockStatement, T data);
+		S? VisitReturnStatement(ReturnStatement returnStatement, T data);
+		S? VisitSwitchStatement(SwitchStatement switchStatement, T data);
+		S? VisitSwitchSection(SwitchSection switchSection, T data);
+		S? VisitCaseLabel(CaseLabel caseLabel, T data);
+		S? VisitSwitchExpression(SwitchExpression switchExpression, T data);
+		S? VisitSwitchExpressionSection(SwitchExpressionSection switchExpressionSection, T data);
+		S? VisitThrowStatement(ThrowStatement throwStatement, T data);
+		S? VisitTryCatchStatement(TryCatchStatement tryCatchStatement, T data);
+		S? VisitCatchClause(CatchClause catchClause, T data);
+		S? VisitUncheckedStatement(UncheckedStatement uncheckedStatement, T data);
+		S? VisitUnsafeStatement(UnsafeStatement unsafeStatement, T data);
+		S? VisitUsingStatement(UsingStatement usingStatement, T data);
+		S? VisitVariableDeclarationStatement(VariableDeclarationStatement variableDeclarationStatement, T data);
+		S? VisitLocalFunctionDeclarationStatement(LocalFunctionDeclarationStatement localFunctionDeclarationStatement, T data);
+		S? VisitWhileStatement(WhileStatement whileStatement, T data);
+		S? VisitYieldBreakStatement(YieldBreakStatement yieldBreakStatement, T data);
+		S? VisitYieldReturnStatement(YieldReturnStatement yieldReturnStatement, T data);
+
+		S? VisitAccessor(Accessor accessor, T data);
+		S? VisitConstructorDeclaration(ConstructorDeclaration constructorDeclaration, T data);
+		S? VisitConstructorInitializer(ConstructorInitializer constructorInitializer, T data);
+		S? VisitDestructorDeclaration(DestructorDeclaration destructorDeclaration, T data);
+		S? VisitEnumMemberDeclaration(EnumMemberDeclaration enumMemberDeclaration, T data);
+		S? VisitEventDeclaration(EventDeclaration eventDeclaration, T data);
+		S? VisitCustomEventDeclaration(CustomEventDeclaration customEventDeclaration, T data);
+		S? VisitFieldDeclaration(FieldDeclaration fieldDeclaration, T data);
+		S? VisitIndexerDeclaration(IndexerDeclaration indexerDeclaration, T data);
+		S? VisitMethodDeclaration(MethodDeclaration methodDeclaration, T data);
+		S? VisitOperatorDeclaration(OperatorDeclaration operatorDeclaration, T data);
+		S? VisitParameterDeclaration(ParameterDeclaration parameterDeclaration, T data);
+		S? VisitPropertyDeclaration(PropertyDeclaration propertyDeclaration, T data);
+		S? VisitVariableInitializer(VariableInitializer variableInitializer, T data);
+		S? VisitFixedFieldDeclaration(FixedFieldDeclaration fixedFieldDeclaration, T data);
+		S? VisitFixedVariableInitializer(FixedVariableInitializer fixedVariableInitializer, T data);
+
+		S? VisitSyntaxTree(SyntaxTree syntaxTree, T data);
+		S? VisitSimpleType(SimpleType simpleType, T data);
+		S? VisitMemberType(MemberType memberType, T data);
+		S? VisitTupleType(TupleAstType tupleType, T data);
+		S? VisitTupleTypeElement(TupleTypeElement tupleTypeElement, T data);
+		S? VisitFunctionPointerType(FunctionPointerAstType functionPointerType, T data);
+		S? VisitInvocationType(InvocationAstType invocationType, T data);
+		S? VisitComposedType(ComposedType composedType, T data);
+		S? VisitArraySpecifier(ArraySpecifier arraySpecifier, T data);
+		S? VisitPrimitiveType(PrimitiveType primitiveType, T data);
+
+		S? VisitComment(Comment comment, T data);
+		S? VisitPreProcessorDirective(PreProcessorDirective preProcessorDirective, T data);
+		S? VisitDocumentationReference(DocumentationReference documentationReference, T data);
+
+		S? VisitTypeParameterDeclaration(TypeParameterDeclaration typeParameterDeclaration, T data);
+		S? VisitConstraint(Constraint constraint, T data);
+		S? VisitCSharpTokenNode(CSharpTokenNode cSharpTokenNode, T data);
+		S? VisitIdentifier(Identifier identifier, T data);
+
+		S? VisitInterpolation(Interpolation interpolation, T data);
+		S? VisitInterpolatedStringText(InterpolatedStringText interpolatedStringText, T data);
+
+		S? VisitSingleVariableDesignation(SingleVariableDesignation singleVariableDesignation, T data);
+		S? VisitParenthesizedVariableDesignation(ParenthesizedVariableDesignation parenthesizedVariableDesignation, T data);
+
+		S? VisitNullNode(AstNode nullNode, T data);
+		S? VisitErrorNode(AstNode errorNode, T data);
+		S? VisitPatternPlaceholder(AstNode placeholder, PatternMatching.Pattern pattern, T data);
 	}
 }

ICSharpCode.Decompiler/CSharp/Syntax/PatternMatching/INode.cs

@@ -25,7 +25,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 	/// </summary>
 	public interface INode
 	{
-		Role Role { get; }
+		Role? Role { get; }
 		INode? FirstChild { get; }
 		INode? NextSibling { get; }
 		bool IsNull { get; }

ICSharpCode.Decompiler/CSharp/Syntax/PatternMatching/Pattern.cs

@@ -52,15 +52,15 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 			get { return false; }
 		}
 
-		Role INode.Role {
+		Role? INode.Role {
 			get { return null; }
 		}
 
-		INode INode.NextSibling {
+		INode? INode.NextSibling {
 			get { return null; }
 		}
 
-		INode INode.FirstChild {
+		INode? INode.FirstChild {
 			get { return null; }
 		}
 
@@ -80,8 +80,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 			stack.Push(new PossibleMatch(firstOtherChild, match.CheckPoint()));
 			while (stack.Count > 0)
 			{
-				INode cur1 = patternStack.Pop();
-				INode cur2 = stack.Peek().NextOther;
+				INode? cur1 = patternStack.Pop();
+				INode? cur2 = stack.Peek().NextOther;
 				match.RestoreCheckPoint(stack.Pop().Checkpoint);
 				bool success = true;
 				while (cur1 != null && success)

ICSharpCode.Decompiler/CSharp/Syntax/PatternMatching/Repeat.cs

@@ -44,7 +44,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 			this.MaxCount = int.MaxValue;
 		}
 
-		public override bool DoMatchCollection(Role role, INode pos, Match match, BacktrackingInfo backtrackingInfo)
+		public override bool DoMatchCollection(Role role, INode? pos, Match match, BacktrackingInfo backtrackingInfo)
 		{
 			var backtrackingStack = backtrackingInfo.backtrackingStack;
 			Debug.Assert(pos == null || pos.Role == role);

ICSharpCode.Decompiler/CSharp/Syntax/Statements/Statement.cs

@@ -63,7 +63,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		#endregion
 
 		#region PatternPlaceholder
-		public static implicit operator Statement(PatternMatching.Pattern pattern)
+		public static implicit operator Statement?(PatternMatching.Pattern? pattern)
 		{
 			return pattern != null ? new PatternPlaceholder(pattern) : null;
 		}
@@ -86,12 +86,12 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				visitor.VisitPatternPlaceholder(this, child);
 			}
 
-			public override T AcceptVisitor<T>(IAstVisitor<T> visitor)
+			public override T? AcceptVisitor<T>(IAstVisitor<T> visitor)
 			{
 				return visitor.VisitPatternPlaceholder(this, child);
 			}
 
-			public override S AcceptVisitor<T, S>(IAstVisitor<T, S> visitor, T data)
+			public override S? AcceptVisitor<T, S>(IAstVisitor<T, S> visitor, T data)
 			{
 				return visitor.VisitPatternPlaceholder(this, child, data);
 			}

ICSharpCode.Decompiler/CSharp/Syntax/SyntaxExtensions.cs

@@ -54,7 +54,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public static Statement GetNextStatement(this Statement statement)
 		{
-			AstNode next = statement.NextSibling;
+			AstNode? next = statement.NextSibling;
 			while (next != null && !(next is Statement))
 				next = next.NextSibling;
 			return (Statement)next;

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/Accessor.cs

@@ -76,7 +76,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// </summary>
 		public CSharpTokenNode Keyword {
 			get {
-				for (AstNode child = this.FirstChild; child != null; child = child.NextSibling)
+				for (AstNode? child = this.FirstChild; child != null; child = child.NextSibling)
 				{
 					if (child.Role == PropertyDeclaration.GetKeywordRole || child.Role == PropertyDeclaration.SetKeywordRole
 						|| child.Role == PropertyDeclaration.InitKeywordRole

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/EntityDeclaration.cs

@@ -89,7 +89,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		internal static void SetModifiers(AstNode node, Modifiers newValue)
 		{
 			Modifiers oldValue = GetModifiers(node);
-			AstNode insertionPos = node.GetChildrenByRole(AttributeRole).LastOrDefault();
+			AstNode? insertionPos = node.GetChildrenByRole(AttributeRole).LastOrDefault();
 			foreach (Modifiers m in CSharpModifierToken.AllModifiers)
 			{
 				if ((m & newValue) != 0)

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/MethodDeclaration.cs

@@ -70,7 +70,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public bool IsExtensionMethod {
 			get {
-				ParameterDeclaration pd = (ParameterDeclaration)GetChildByRole(Roles.Parameter);
+				ParameterDeclaration? pd = GetChildByRole(Roles.Parameter) as ParameterDeclaration;
 				return pd != null && pd.HasThisModifier;
 			}
 		}

ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

@@ -462,13 +462,13 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		AstType ConvertTypeHelper(IType genericType, IReadOnlyList<IType> typeArguments)
 		{
-			ITypeDefinition typeDef = genericType.GetDefinition();
+			ITypeDefinition? typeDef = genericType.GetDefinition();
 			Debug.Assert(typeDef != null || genericType.Kind == TypeKind.Unknown);
 			Debug.Assert(typeArguments.Count >= genericType.TypeParameterCount);
 
 			if (UseKeywordsForBuiltinTypes && typeDef != null)
 			{
-				string keyword = KnownTypeReference.GetCSharpNameByTypeCode(typeDef.KnownTypeCode);
+				string? keyword = KnownTypeReference.GetCSharpNameByTypeCode(typeDef.KnownTypeCode);
 				if (keyword != null)
 				{
 					return new PrimitiveType(keyword);
@@ -1053,7 +1053,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 					}
 					if (underlyingType.IsKnownType(KnownTypeCode.Double) || underlyingType.IsKnownType(KnownTypeCode.Single))
 						return ConvertFloatingPointLiteral(underlyingType, constantValue);
-					IType literalType = underlyingType;
+					IType? literalType = underlyingType;
 					bool integerTypeMismatch = underlyingType.IsCSharpSmallIntegerType() || underlyingType.IsCSharpNativeIntegerType();
 					if (integerTypeMismatch)
 					{
@@ -1213,7 +1213,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		Expression ConvertEnumValue(IType type, long val)
 		{
-			ITypeDefinition enumDefinition = type.GetDefinition();
+			ITypeDefinition? enumDefinition = type.GetDefinition();
 			TypeCode enumBaseTypeCode = ReflectionHelper.GetTypeCode(enumDefinition.EnumUnderlyingType);
 			var fields = enumDefinition.Fields
 				.Select(PrepareConstant)
@@ -1295,7 +1295,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			{
 				if (!field.IsConst)
 					return (-1, null);
-				object constantValue = field.GetConstantValue();
+				object? constantValue = field.GetConstantValue();
 				if (constantValue == null)
 					return (-1, null);
 				return ((long)CSharpPrimitiveCast.Cast(TypeCode.Int64, constantValue, checkForOverflow: false), field);
@@ -1890,7 +1890,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		DelegateDeclaration ConvertDelegate(IMethod invokeMethod, Modifiers modifiers)
 		{
-			ITypeDefinition d = invokeMethod.DeclaringTypeDefinition;
+			ITypeDefinition? d = invokeMethod.DeclaringTypeDefinition;
 
 			DelegateDeclaration decl = new DelegateDeclaration();
 			decl.Modifiers = modifiers & ~Modifiers.Sealed;
@@ -2019,7 +2019,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				decl.Modifiers = ModifierFromAccessibility(accessor.Accessibility);
 			if (this.ShowModifiers && accessor.HasReadonlyModifier())
 				decl.Modifiers |= Modifiers.Readonly;
-			TokenRole keywordRole = kind switch {
+			TokenRole? keywordRole = kind switch {
 				MethodSemanticsAttributes.Getter => PropertyDeclaration.GetKeywordRole,
 				MethodSemanticsAttributes.Setter => PropertyDeclaration.SetKeywordRole,
 				MethodSemanticsAttributes.Adder => CustomEventDeclaration.AddKeywordRole,
@@ -2460,7 +2460,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		static bool IsObjectOrValueType(IType type)
 		{
-			ITypeDefinition d = type.GetDefinition();
+			ITypeDefinition? d = type.GetDefinition();
 			return d != null && (d.KnownTypeCode == KnownTypeCode.Object || d.KnownTypeCode == KnownTypeCode.ValueType);
 		}
 		#endregion

ICSharpCode.Decompiler/CSharp/Transforms/AddCheckedBlocks.cs

@@ -244,7 +244,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			BlockStatement? block = node as BlockStatement;
 			if (block == null)
 			{
-				for (AstNode child = node.FirstChild; child != null; child = child.NextSibling)
+				for (AstNode? child = node.FirstChild; child != null; child = child.NextSibling)
 				{
 					Run(child, context);
 				}
@@ -275,7 +275,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			InsertedNode? nodesUncheckedContextCheckedBlockOpen = null;
 			Statement? checkedBlockStart = null;
 
-			Statement statement = block.Statements.FirstOrDefault();
+			Statement? statement = block.Statements.FirstOrDefault();
 			while (true)
 			{
 				// Blocks can be closed 'for free'. We use '<=' so that blocks are closed as late as possible (goal 4b)
@@ -340,7 +340,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			if (node is BlockStatement)
 				return GetResultFromBlock((BlockStatement)node);
 			Result result = new Result();
-			for (AstNode child = node.FirstChild; child != null; child = child.NextSibling)
+			for (AstNode? child = node.FirstChild; child != null; child = child.NextSibling)
 			{
 				Result childResult = GetResult(child);
 				result.CostInCheckedContext += childResult.CostInCheckedContext;

ICSharpCode.Decompiler/CSharp/Transforms/AddXmlDocumentationTransform.cs

@@ -63,7 +63,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		static void InsertXmlDocumentation(AstNode node, StringReader r)
 		{
 			// Find the first non-empty line:
-			string firstLine;
+			string? firstLine;
 			do
 			{
 				firstLine = r.ReadLine();
@@ -71,7 +71,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					return;
 			} while (string.IsNullOrWhiteSpace(firstLine));
 			string indentation = firstLine.Substring(0, firstLine.Length - firstLine.TrimStart().Length);
-			string line = firstLine;
+			string? line = firstLine;
 			int skippedWhitespaceLines = 0;
 			// Copy all lines from input to output, except for empty lines at the end.
 			while (line != null)

ICSharpCode.Decompiler/CSharp/Transforms/CombineQueryExpressions.cs

@@ -47,8 +47,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 
 		void CombineQueries(AstNode node, Dictionary<string, object> fromOrLetIdentifiers)
 		{
-			AstNode next;
-			for (AstNode child = node.FirstChild; child != null; child = next)
+			AstNode? next;
+			for (AstNode? child = node.FirstChild; child != null; child = next)
 			{
 				// store reference to next child before transformation
 				next = child.NextSibling;

ICSharpCode.Decompiler/CSharp/Transforms/DeclareVariables.cs

@@ -297,7 +297,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 			try
 			{
-				for (AstNode child = node.FirstChild; child != null; child = child.NextSibling)
+				for (AstNode? child = node.FirstChild; child != null; child = child.NextSibling)
 				{
 					FindInsertionPoints(child, nodeLevel + 1);
 				}
@@ -321,7 +321,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					{
 						InsertionPoint newPoint;
 						int startIndex = scopeTracking.Count - 1;
-						BlockContainer captureScope = variable.CaptureScope;
+						BlockContainer? captureScope = variable.CaptureScope;
 						while (captureScope != null && !IsRelevantScope(captureScope))
 						{
 							captureScope = BlockContainer.FindClosestContainer(captureScope.Parent);
@@ -356,7 +356,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 								}
 							}
 						}
-						if (variableDict.TryGetValue(variable, out VariableToDeclare v))
+						if (variableDict.TryGetValue(variable, out VariableToDeclare? v))
 						{
 							v.InsertionPoint = FindCommonParent(v.InsertionPoint, newPoint);
 						}

ICSharpCode.Decompiler/CSharp/Transforms/FixNameCollisions.cs

@@ -67,8 +67,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			{
 				if (node is IdentifierExpression || node is MemberReferenceExpression)
 				{
-					ISymbol symbol = node.GetSymbol();
-					if (symbol != null && renamedSymbols.TryGetValue(symbol, out string newName))
+					ISymbol? symbol = node.GetSymbol();
+					if (symbol != null && renamedSymbols.TryGetValue(symbol, out string? newName))
 					{
 						node.GetChildByRole(Roles.Identifier).Name = newName;
 					}

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceQueryExpressions.cs

@@ -88,8 +88,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				node.ReplaceWith(query);
 			}
 
-			AstNode next;
-			for (AstNode child = (query ?? node).FirstChild; child != null; child = next)
+			AstNode? next;
+			for (AstNode? child = (query ?? node).FirstChild; child != null; child = next)
 			{
 				// store reference to next child before transformation
 				next = child.NextSibling;
@@ -103,7 +103,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			return context.Settings.Discards;
 		}
 
-		QueryExpression DecompileQuery(InvocationExpression invocation)
+		QueryExpression? DecompileQuery(InvocationExpression? invocation)
 		{
 			if (invocation == null)
 				return null;
@@ -119,7 +119,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					if (!IsComplexQuery(mre))
 						return null;
 					Expression expr = invocation.Arguments.Single();
-					if (MatchSimpleLambda(expr, out ParameterDeclaration parameter, out Expression body))
+					if (MatchSimpleLambda(expr, out ParameterDeclaration? parameter, out Expression? body))
 					{
 						QueryExpression query = new QueryExpression();
 						query.Clauses.Add(MakeFromClause(parameter, mre.Target.Detach()));
@@ -134,8 +134,8 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					{
 						Expression keyLambda = invocation.Arguments.ElementAt(0);
 						Expression projectionLambda = invocation.Arguments.ElementAt(1);
-						if (MatchSimpleLambda(keyLambda, out ParameterDeclaration parameter1, out Expression keySelector)
-							&& MatchSimpleLambda(projectionLambda, out ParameterDeclaration parameter2, out Expression elementSelector)
+						if (MatchSimpleLambda(keyLambda, out ParameterDeclaration? parameter1, out Expression? keySelector)
+							&& MatchSimpleLambda(projectionLambda, out ParameterDeclaration? parameter2, out Expression? elementSelector)
 							&& parameter1.Name == parameter2.Name)
 						{
 							QueryExpression query = new QueryExpression();
@@ -152,7 +152,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					else if (invocation.Arguments.Count == 1)
 					{
 						Expression lambda = invocation.Arguments.Single();
-						if (MatchSimpleLambda(lambda, out ParameterDeclaration parameter, out Expression keySelector))
+						if (MatchSimpleLambda(lambda, out ParameterDeclaration? parameter, out Expression? keySelector))
 						{
 							QueryExpression query = new QueryExpression();
 							query.Clauses.Add(MakeFromClause(parameter, mre.Target.Detach()));
@@ -167,7 +167,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					if (invocation.Arguments.Count != 2)
 						return null;
 					var fromExpressionLambda = invocation.Arguments.ElementAt(0);
-					if (!MatchSimpleLambda(fromExpressionLambda, out ParameterDeclaration parameter, out Expression collectionSelector))
+					if (!MatchSimpleLambda(fromExpressionLambda, out ParameterDeclaration? parameter, out Expression? collectionSelector))
 						return null;
 					if (IsNullConditional(collectionSelector))
 						return null;
@@ -194,7 +194,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					if (!IsComplexQuery(mre))
 						return null;
 					Expression expr = invocation.Arguments.Single();
-					if (MatchSimpleLambda(expr, out ParameterDeclaration parameter, out Expression body))
+					if (MatchSimpleLambda(expr, out ParameterDeclaration? parameter, out Expression? body))
 					{
 						QueryExpression query = new QueryExpression();
 						query.Clauses.Add(MakeFromClause(parameter, mre.Target.Detach()));
@@ -213,7 +213,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					if (!IsComplexQuery(mre))
 						return null;
 					var lambda = invocation.Arguments.Single();
-					if (MatchSimpleLambda(lambda, out ParameterDeclaration parameter, out Expression orderExpression))
+					if (MatchSimpleLambda(lambda, out ParameterDeclaration? parameter, out Expression? orderExpression))
 					{
 						if (ValidateThenByChain(invocation, parameter.Name))
 						{
@@ -257,10 +257,10 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					if (IsNullConditional(source2))
 						return null;
 					Expression outerLambda = invocation.Arguments.ElementAt(1);
-					if (!MatchSimpleLambda(outerLambda, out ParameterDeclaration element1, out Expression key1))
+					if (!MatchSimpleLambda(outerLambda, out ParameterDeclaration? element1, out Expression? key1))
 						return null;
 					Expression innerLambda = invocation.Arguments.ElementAt(2);
-					if (!MatchSimpleLambda(innerLambda, out ParameterDeclaration element2, out Expression key2))
+					if (!MatchSimpleLambda(innerLambda, out ParameterDeclaration? element2, out Expression? key2))
 						return null;
 					LambdaExpression? lambda = invocation.Arguments.ElementAt(3) as LambdaExpression;
 					if (lambda != null && lambda.Parameters.Count == 2 && lambda.Body is Expression)

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -62,7 +62,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			// Go through the children, and keep visiting a node as long as it changes.
 			// Because some transforms delete/replace nodes before and after the node being transformed, we rely
 			// on the transform's return value to know where we need to keep iterating.
-			for (AstNode child = node.FirstChild; child != null; child = child.NextSibling)
+			for (AstNode? child = node.FirstChild; child != null; child = child.NextSibling)
 			{
 				AstNode oldChild;
 				do
@@ -88,7 +88,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 
 		public override AstNode VisitForStatement(ForStatement forStatement)
 		{
-			AstNode result = TransformForeachOnArray(forStatement);
+			AstNode? result = TransformForeachOnArray(forStatement);
 			if (result != null)
 				return result;
 			return base.VisitForStatement(forStatement);
@@ -174,7 +174,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 		};
 
-		public ForStatement TransformFor(ExpressionStatement node)
+		public ForStatement? TransformFor(ExpressionStatement node)
 		{
 			if (!context.Settings.ForStatement)
 				return null;
@@ -339,7 +339,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			return false;
 		}
 
-		Statement TransformForeachOnArray(ForStatement forStatement)
+		Statement? TransformForeachOnArray(ForStatement forStatement)
 		{
 			if (!context.Settings.ForEachStatement)
 				return null;

ICSharpCode.Decompiler/CSharp/Transforms/TransformFieldAndConstructorInitializers.cs

@@ -206,7 +206,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 					Match m = fieldInitializerPattern.Match(instanceCtorsNotChainingWithThis[0].Body.FirstOrDefault());
 					if (!m.Success)
 						break;
-					IMember fieldOrPropertyOrEvent = (m.Get<AstNode>("fieldAccess").Single().GetSymbol() as IMember)?.MemberDefinition;
+					IMember? fieldOrPropertyOrEvent = (m.Get<AstNode>("fieldAccess").Single().GetSymbol() as IMember)?.MemberDefinition;
 					if (!(fieldOrPropertyOrEvent is IField) && !(fieldOrPropertyOrEvent is IProperty) && !(fieldOrPropertyOrEvent is IEvent))
 						break;
 					var fieldOrPropertyOrEventDecl = members.FirstOrDefault(f => f.GetSymbol() == fieldOrPropertyOrEvent) as EntityDeclaration;
@@ -346,7 +346,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 						AssignmentExpression? assignment = es.Expression as AssignmentExpression;
 						if (assignment == null || assignment.Operator != AssignmentOperatorType.Assign)
 							break;
-						IMember fieldOrProperty = (assignment.Left.GetSymbol() as IMember)?.MemberDefinition;
+						IMember? fieldOrProperty = (assignment.Left.GetSymbol() as IMember)?.MemberDefinition;
 						if (!(fieldOrProperty is IField || fieldOrProperty is IProperty) || !fieldOrProperty.IsStatic)
 							break;
 						// Only move fields that are constants, if the declaring type is not marked beforefieldinit.

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -156,7 +156,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			if (descendant == Expression)
 				return this;
-			for (AstNode parent = descendant.Parent; parent != null; parent = parent.Parent)
+			for (AstNode? parent = descendant.Parent; parent != null; parent = parent.Parent)
 			{
 				foreach (var inst in parent.Annotations.OfType<ILInstruction>())
 					descendant.AddAnnotation(inst);

ICSharpCode.Decompiler/CSharp/TypeSystem/ResolvedUsingScope.cs

@@ -70,7 +70,7 @@ namespace ICSharpCode.Decompiler.CSharp.TypeSystem
 
 		public INamespace Namespace {
 			get {
-				INamespace result = LazyInit.VolatileRead(ref this.@namespace);
+				INamespace? result = LazyInit.VolatileRead(ref this.@namespace);
 				if (result != null)
 				{
 					return result;

ICSharpCode.Decompiler/DecompilerException.cs

@@ -98,7 +98,7 @@ namespace ICSharpCode.Decompiler
 
 		static string GetTypeName(Exception exception)
 		{
-			string type = exception.GetType().FullName;
+			string? type = exception.GetType().FullName;
 			if (exception is ExternalException || exception is IOException)
 				return type + " (" + Marshal.GetHRForException(exception).ToString("x8") + ")";
 			else
@@ -114,8 +114,8 @@ namespace ICSharpCode.Decompiler
 			StringBuilder b = new StringBuilder();
 			for (int i = 0; i < stackTrace.FrameCount; i++)
 			{
-				StackFrame frame = stackTrace.GetFrame(i);
-				MethodBase method = frame.GetMethod();
+				StackFrame? frame = stackTrace.GetFrame(i);
+				MethodBase? method = frame.GetMethod();
 				if (method == null)
 					continue;
 
@@ -123,7 +123,7 @@ namespace ICSharpCode.Decompiler
 					b.AppendLine();
 
 				b.Append("   at ");
-				Type declaringType = method.DeclaringType;
+				Type? declaringType = method.DeclaringType;
 				if (declaringType != null)
 				{
 					b.Append(declaringType.FullName.Replace('+', '.'));
@@ -173,7 +173,7 @@ namespace ICSharpCode.Decompiler
 					string? filename = null;
 					try
 					{
-						string fullpath = frame.GetFileName();
+						string? fullpath = frame.GetFileName();
 						if (fullpath != null)
 							filename = Path.GetFileName(fullpath);
 					}

ICSharpCode.Decompiler/Disassembler/ReflectionDisassembler.cs

@@ -1040,10 +1040,10 @@ namespace ICSharpCode.Decompiler.Disassembler
 					output.Write("lpstruct");
 					break;
 				case 0x2c: // CustomMarshaler
-					string guidValue = blob.ReadSerializedString();
-					string unmanagedType = blob.ReadSerializedString();
-					string managedType = blob.ReadSerializedString();
-					string cookie = blob.ReadSerializedString();
+					string? guidValue = blob.ReadSerializedString();
+					string? unmanagedType = blob.ReadSerializedString();
+					string? managedType = blob.ReadSerializedString();
+					string? cookie = blob.ReadSerializedString();
 
 					var guid = !string.IsNullOrEmpty(guidValue) ? new Guid(guidValue) : Guid.Empty;
 

ICSharpCode.Decompiler/Documentation/GetPotentiallyNestedClassTypeReference.cs

@@ -57,7 +57,7 @@ namespace ICSharpCode.Decompiler.Documentation
 				{
 					if (asm == null)
 						continue;
-					ITypeDefinition typeDef = asm.GetTypeDefinition(new TopLevelTypeName(ns, name, topLevelTPC));
+					ITypeDefinition? typeDef = asm.GetTypeDefinition(new TopLevelTypeName(ns, name, topLevelTPC));
 					for (int j = i + 1; j < parts.Length && typeDef != null; j++)
 					{
 						int tpc = (j == parts.Length - 1 ? typeParameterCount : 0);

ICSharpCode.Decompiler/Documentation/IdStringProvider.cs

@@ -155,7 +155,7 @@ namespace ICSharpCode.Decompiler.Documentation
 					b.Append('@');
 					break;
 				default:
-					IType declType = type.DeclaringType;
+					IType? declType = type.DeclaringType;
 					if (declType != null)
 					{
 						AppendTypeName(b, declType, explicitInterfaceImpl);

ICSharpCode.Decompiler/Documentation/XmlDocLoader.cs

@@ -54,7 +54,7 @@ namespace ICSharpCode.Decompiler.Documentation
 				throw new ArgumentNullException(nameof(module));
 			lock (cache)
 			{
-				if (!cache.TryGetValue(module, out XmlDocumentationProvider xmlDoc))
+				if (!cache.TryGetValue(module, out XmlDocumentationProvider? xmlDoc))
 				{
 					string xmlDocFile = LookupLocalizedXmlDoc(module.FileName);
 					if (xmlDocFile == null)

ICSharpCode.Decompiler/IL/ControlFlow/AsyncAwaitDecompiler.cs

@@ -1084,8 +1084,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 
 		bool IsBuilderFieldOnThis(ILInstruction inst)
 		{
-			IField field;
-			ILInstruction target;
+			IField? field;
+			ILInstruction? target;
 			if (builderType.IsReferenceType == true)
 			{
 				// ldfld(StateMachine::<>t__builder, ldloc(this))

ICSharpCode.Decompiler/IL/ControlFlow/AwaitInCatchTransform.cs

@@ -102,7 +102,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 							break;
 						case SwitchSection jumpTableEntry:
 							Debug.Assert(switchInstructionOpt == null || jumpTableEntry.Parent == switchInstructionOpt);
-							switchInstructionOpt = (SwitchInstruction)jumpTableEntry.Parent;
+							switchInstructionOpt = jumpTableEntry.Parent as SwitchInstruction;
 							break;
 					}
 
@@ -142,7 +142,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 					if (result.NextBlockOrExitContainer is Block nextBlock && nextBlock.IncomingEdgeCount == 0)
 					{
 						List<Block> dependentBlocks = new List<Block>();
-						Block current = nextBlock;
+						Block? current = nextBlock;
 
 						do
 						{
@@ -201,8 +201,8 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		{
 			ILVariable? v = null;
 			if (MatchExceptionCaptureBlock(context, block,
-				ref v, out StLoc typedExceptionVariableStore,
-				out Block captureBlock, out Block throwBlock))
+				ref v, out StLoc? typedExceptionVariableStore,
+				out Block? captureBlock, out Block? throwBlock))
 			{
 				context.Step($"ExceptionDispatchInfo.Capture({v.Name}).Throw() => throw;", typedExceptionVariableStore);
 				block.Instructions.RemoveRange(typedExceptionVariableStore.ChildIndex + 1, 2);
@@ -355,7 +355,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				return false;
 			}
 
-			bool ParseIfJumpTable(int id, Block jumpTableEntryBlock, ILVariable identifierVariable, out Block? realEntryPoint, out ILInstruction? nextBlockOrExitContainer, out ILInstruction? jumpTableEntry)
+			bool ParseIfJumpTable(int id, Block jumpTableEntryBlock, ILVariable identifierVariable, [NotNullWhen(true)] out Block? realEntryPoint, out ILInstruction? nextBlockOrExitContainer, [NotNullWhen(true)] out ILInstruction? jumpTableEntry)
 			{
 				realEntryPoint = null;
 				nextBlockOrExitContainer = null;
@@ -420,7 +420,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		// =>
 		// throw(ldloc result.Handler.Variable)
 		internal static bool MatchExceptionCaptureBlock(ILTransformContext context, Block block,
-			ref ILVariable objectVariable, out StLoc? typedExceptionVariableStore, out Block? captureBlock, out Block? throwBlock)
+			ref ILVariable? objectVariable, out StLoc? typedExceptionVariableStore, out Block? captureBlock, out Block? throwBlock)
 		{
 			bool DerivesFromException(IType t) => t.GetAllBaseTypes().Any(ty => ty.IsKnownType(KnownTypeCode.Exception));
 

ICSharpCode.Decompiler/IL/ControlFlow/AwaitInFinallyTransform.cs

@@ -81,7 +81,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				// stloc V_6(ldloc V_3)	- store exception in 'global' object variable
 				// br IL_0075				- jump out of catch block to the head of the finallyBlock
 				var catchBlockEntry = catchBlockContainer.EntryPoint;
-				ILVariable objectVariable;
+				ILVariable? objectVariable;
 				switch (catchBlockEntry.Instructions.Count)
 				{
 					case 2:
@@ -127,7 +127,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 
 				StateRangeAnalysis sra = new StateRangeAnalysis(StateRangeAnalysisMode.AwaitInFinally, null, stateVariable);
 				sra.AssignStateRanges(noThrowBlock, Util.LongSet.Universe);
-				var mapping = sra.GetBlockStateSetMapping((BlockContainer)noThrowBlock.Parent);
+				var mapping = sra.GetBlockStateSetMapping(noThrowBlock.Parent as BlockContainer);
 				var mappingForLeave = sra.GetBlockStateSetMappingForLeave();
 
 				context.StepStartGroup("Inline finally block with await", tryCatch.Handlers[0]);

ICSharpCode.Decompiler/IL/ControlFlow/ConditionDetection.cs

@@ -45,9 +45,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			Other
 		}
 
-		private BlockTransformContext context;
-		private ControlFlowNode cfgNode;
-		private BlockContainer currentContainer;
+		private BlockTransformContext? context;
+		private ControlFlowNode? cfgNode;
+		private BlockContainer? currentContainer;
 
 		/// <summary>
 		/// Builds structured control flow for the block associated with the control flow node.
@@ -59,7 +59,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 		public void Run(Block block, BlockTransformContext context)
 		{
 			this.context = context;
-			currentContainer = (BlockContainer)block.Parent;
+			currentContainer = block.Parent as BlockContainer;
 
 			// We only embed blocks into this block if they aren't referenced anywhere else,
 			// so those blocks are dominated by this block.

ICSharpCode.Decompiler/IL/ControlFlow/ControlFlowSimplification.cs

@@ -120,11 +120,11 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			// (where 'v' has no other uses)
 			// Simplify these to a simple `ret(<inst>)` so that they match the release build version.
 			// 
-			if (block.Instructions.Count == 2 && block.Instructions[1].MatchReturn(out ILInstruction value))
+			if (block.Instructions.Count == 2 && block.Instructions[1].MatchReturn(out ILInstruction? value))
 			{
 				var ret = (Leave)block.Instructions[1];
-				if (value.MatchLdLoc(out ILVariable v)
-					&& v.IsSingleDefinition && v.LoadCount == 1 && block.Instructions[0].MatchStLoc(v, out ILInstruction inst))
+				if (value.MatchLdLoc(out ILVariable? v)
+					&& v.IsSingleDefinition && v.LoadCount == 1 && block.Instructions[0].MatchStLoc(v, out ILInstruction? inst))
 				{
 					context.Step("Inline variable in return block", block);
 					inst.AddILRange(ret.Value);
@@ -228,7 +228,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 			if (!value.MatchLdLoc(out var returnVar))
 				return false;
 			var container = branch.TargetContainer;
-			for (ILInstruction inst = branch; inst != container; inst = inst.Parent)
+			for (ILInstruction? inst = branch; inst != container; inst = inst.Parent)
 			{
 				if (inst.Parent is TryFinally tryFinally && inst.SlotInfo == TryFinally.TryBlockSlot)
 				{

ICSharpCode.Decompiler/IL/ControlFlow/DetectPinnedRegions.cs

@@ -106,7 +106,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
 				for (int j = 0; j < block.Instructions.Count - 1; j++)
 				{
 					var inst = block.Instructions[j];
-					if (inst.MatchStLoc(out ILVariable v, out var value) && v.Kind == VariableKind.PinnedLocal)
+					if (inst.MatchStLoc(out ILVariable? v, out var value) && v.Kind == VariableKind.PinnedLocal)
 					{
 						if (block.Instructions[j + 1].OpCode != OpCode.Branch)
 						{

ICSharpCode.Decompiler/IL/Transforms/CachedDelegateInitialization.cs

@@ -88,9 +88,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			if (trueInst == null || trueInst.Instructions.Count != 1 || !inst.FalseInst.MatchNop())
 				return false;
 			var storeInst = trueInst.Instructions[0];
-			if (!inst.Condition.MatchCompEquals(out ILInstruction left, out ILInstruction right) || !left.MatchLdsFld(out IField field) || !right.MatchLdNull())
+			if (!inst.Condition.MatchCompEquals(out ILInstruction? left, out ILInstruction? right) || !left.MatchLdsFld(out IField? field) || !right.MatchLdNull())
 				return false;
-			if (!storeInst.MatchStsFld(out IField field2, out ILInstruction value) || !field.Equals(field2) || !field.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
+			if (!storeInst.MatchStsFld(out IField? field2, out ILInstruction? value) || !field.Equals(field2) || !field.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
 				return false;
 			if (!DelegateConstruction.MatchDelegateConstruction(value.UnwrapConv(ConversionKind.Invalid) as NewObj, out _, out _, out _, true))
 				return false;
@@ -117,10 +117,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			Block? trueInst = inst.TrueInst as Block;
 			if (trueInst == null || (trueInst.Instructions.Count != 1) || !inst.FalseInst.MatchNop())
 				return false;
-			if (!inst.Condition.MatchCompEquals(out ILInstruction left, out ILInstruction right) || !left.MatchLdLoc(out ILVariable v) || !right.MatchLdNull())
+			if (!inst.Condition.MatchCompEquals(out ILInstruction? left, out ILInstruction? right) || !left.MatchLdLoc(out ILVariable? v) || !right.MatchLdNull())
 				return false;
 			var storeInst = trueInst.Instructions.Last();
-			if (!storeInst.MatchStLoc(v, out ILInstruction value))
+			if (!storeInst.MatchStLoc(v, out ILInstruction? value))
 				return false;
 			if (!DelegateConstruction.MatchDelegateConstruction(value as NewObj, out _, out _, out _, true))
 				return false;
@@ -157,7 +157,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			Block? trueInst = inst.TrueInst as Block;
 			if (trueInst == null || (trueInst.Instructions.Count != 1) || !inst.FalseInst.MatchNop())
 				return false;
-			if (!inst.Condition.MatchCompEquals(out ILInstruction left, out ILInstruction right) || !left.MatchLdLoc(out ILVariable s) || !right.MatchLdNull())
+			if (!inst.Condition.MatchCompEquals(out ILInstruction? left, out ILInstruction? right) || !left.MatchLdLoc(out ILVariable? s) || !right.MatchLdNull())
 				return false;
 			var storeInst = trueInst.Instructions.Last() as StLoc;
 			var storeBeforeIf = inst.Parent.Children.ElementAtOrDefault(inst.ChildIndex - 1) as StLoc;
@@ -189,7 +189,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			Block? trueInst = inst.TrueInst as Block;
 			if (trueInst == null || (trueInst.Instructions.Count != 1) || !inst.FalseInst.MatchNop())
 				return false;
-			if (!inst.Condition.MatchCompEquals(out ILInstruction left, out ILInstruction right) || !left.MatchLdLoc(out ILVariable s) || !right.MatchLdNull())
+			if (!inst.Condition.MatchCompEquals(out ILInstruction? left, out ILInstruction? right) || !left.MatchLdLoc(out ILVariable? s) || !right.MatchLdNull())
 				return false;
 			var storeInst = trueInst.Instructions.Last() as StLoc;
 			var storeBeforeIf = inst.Parent.Children.ElementAtOrDefault(inst.ChildIndex - 1) as StLoc;
@@ -240,7 +240,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				return false;
 			}
-			if (!inst.Condition.MatchCompEquals(out ILInstruction left, out ILInstruction right) || !right.MatchLdNull())
+			if (!inst.Condition.MatchCompEquals(out ILInstruction? left, out ILInstruction? right) || !right.MatchLdNull())
 				return false;
 			if (!ldobj.Match(left).Success)
 				return false;
@@ -311,7 +311,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			{
 				return false;
 			}
-			if (!inst.Condition.MatchCompNotEqualsNull(out ILInstruction left))
+			if (!inst.Condition.MatchCompNotEqualsNull(out ILInstruction? left))
 				return false;
 			if (!ldobj.Match(left).Success)
 				return false;

ICSharpCode.Decompiler/IL/Transforms/CopyPropagation.cs

@@ -65,7 +65,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			for (int i = 0; i < block.Instructions.Count; i++)
 			{
-				if (block.Instructions[i].MatchStLoc(out ILVariable v, out ILInstruction copiedExpr))
+				if (block.Instructions[i].MatchStLoc(out ILVariable? v, out ILInstruction? copiedExpr))
 				{
 					if (v.IsSingleDefinition && v.LoadCount == 0 && v.Kind == VariableKind.StackSlot)
 					{

ICSharpCode.Decompiler/IL/Transforms/EarlyExpressionTransforms.cs

@@ -104,7 +104,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		// This transform is required because ILInlining only works with stloc/ldloc
 		internal static bool StObjToStLoc(StObj inst, ILTransformContext context)
 		{
-			if (inst.Target.MatchLdLoca(out ILVariable v)
+			if (inst.Target.MatchLdLoca(out ILVariable? v)
 				&& TypeUtils.IsCompatibleTypeForMemoryAccess(v.Type, inst.Type)
 				&& inst.UnalignedPrefix == 0
 				&& !inst.IsVolatile)
@@ -222,6 +222,5 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 			return false;
 		}
-
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/IndexRangeTransform.cs

@@ -38,7 +38,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			if (!context.Settings.Ranges)
 				return false;
-			if (!ldelema.Array.MatchLdLoc(out ILVariable array))
+			if (!ldelema.Array.MatchLdLoc(out ILVariable? array))
 				return false;
 			if (ldelema.Indices.Count != 1)
 				return false; // the index/range feature doesn't support multi-dimensional arrays
@@ -176,7 +176,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 
 			// stloc startOffsetVar(call GetOffset(startIndexLoad, ldloc length))
-			if (!(block.Instructions[pos].MatchStLoc(out ILVariable startOffsetVar, out ILInstruction startOffsetVarInit)
+			if (!(block.Instructions[pos].MatchStLoc(out ILVariable? startOffsetVar, out ILInstruction? startOffsetVarInit)
 				&& startOffsetVar.IsSingleDefinition && startOffsetVar.StackType == StackType.I4))
 			{
 				// Not our primary indexing/slicing pattern.

ICSharpCode.Decompiler/IL/Transforms/SwitchOnStringTransform.cs

@@ -106,9 +106,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				context.Step("Remove hashtable initializer", actual);
 				if (jumpToNext != null)
 				{
-					actual.Instructions.SecondToLastOrDefault().ReplaceWith(jumpToNext);
+					actual.Instructions.SecondToLastOrDefault()?.ReplaceWith(jumpToNext);
 				}
-				actual.Instructions.LastOrDefault().ReplaceWith(new Branch(next));
+				actual.Instructions.LastOrDefault()?.ReplaceWith(new Branch(next));
 				omittedBlocks.Add(containingBlock, previous);
 				changedContainers.Add(body);
 			}
@@ -196,7 +196,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				ExtensionMethods.Swap(ref firstBlockOrDefaultJump, ref nextCaseJump);
 			}
 			// match call to operator ==(string, string)
-			if (!MatchStringEqualityComparison(condition, out var switchValueVar, out string firstBlockValue, out bool isVBCompareString))
+			if (!MatchStringEqualityComparison(condition, out var switchValueVar, out string? firstBlockValue, out bool isVBCompareString))
 				return false;
 			if (isVBCompareString)
 			{
@@ -217,13 +217,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			}
 
-			var values = new List<(string, ILInstruction)>();
-			var uniqueValues = new HashSet<string>();
+			var values = new List<(string?, ILInstruction)>();
+			var uniqueValues = new HashSet<string?>();
 			int numberOfUniqueMatchesWithCurrentVariable = 0;
 			HashSet<Block> caseBlocks = new HashSet<Block>();
 			caseBlocks.Add((Block)instructions[i].Parent);
 
-			bool AddSwitchSection(string value, ILInstruction inst)
+			bool AddSwitchSection(string? value, ILInstruction inst)
 			{
 				if (!uniqueValues.Add(value))
 					return false;
@@ -306,14 +306,14 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				}
 			}
 			// if instruction must be followed by a branch to the next case
-			if (!nextCaseJump.MatchBranch(out Block currentCaseBlock))
+			if (!nextCaseJump.MatchBranch(out Block? currentCaseBlock))
 				return false;
 			// extract all cases and add them to the values list.
 			ILInstruction nextCaseBlock;
 			do
 			{
-				nextCaseBlock = MatchCaseBlock(currentCaseBlock, switchValueVar, out string value, out bool emptyStringEqualsNull, out ILInstruction block);
-				if (nextCaseBlock == null)
+				(nextCaseBlock, var block) = MatchCaseBlock(currentCaseBlock, switchValueVar, out string? value, out bool emptyStringEqualsNull);
+				if (nextCaseBlock == null || block == null)
 					break;
 				if (emptyStringEqualsNull && string.IsNullOrEmpty(value))
 				{
@@ -474,7 +474,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool IsIsInternedCall(Call call, [NotNullWhen(true)] out ILInstruction? argument)
+		bool IsIsInternedCall(Call? call, [NotNullWhen(true)] out ILInstruction? argument)
 		{
 			if (call != null
 				&& call.Method.DeclaringType.IsKnownType(KnownTypeCode.String)
@@ -504,19 +504,20 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// The <paramref name="switchVariable"/> is updated if the value gets copied to a different variable.
 		/// See comments below for more info.
 		/// </summary>
-		ILInstruction? MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string? value, out bool emptyStringEqualsNull, out ILInstruction? caseBlockOrLeave)
+
+		(ILInstruction? NextBlock, ILInstruction? CaseBlockOrLeave) MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string? value, out bool emptyStringEqualsNull)
 		{
 			value = null;
-			caseBlockOrLeave = null;
+			ILInstruction? caseBlockOrLeave = null;
 			emptyStringEqualsNull = false;
 
 			if (currentBlock.IncomingEdgeCount != 1 || currentBlock.Instructions.Count != 2)
-				return null;
+				return (null, null);
 			if (!currentBlock.MatchIfAtEndOfBlock(out var condition, out var caseBlockBranch, out var nextBlockBranch))
-				return null;
+				return (null, null);
 			if (!MatchStringEqualityComparison(condition, switchVariable, out value, out bool isVBCompareString))
 			{
-				return null;
+				return (null, null);
 			}
 			if (isVBCompareString)
 			{
@@ -533,21 +534,21 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 			else
 			{
-				return null;
+				return (null, null);
 			}
 			if (nextBlockBranch.MatchBranch(out Block? nextBlock))
 			{
 				// success
-				return nextBlock;
+				return (nextBlock, caseBlockOrLeave);
 			}
 			else if (nextBlockBranch.MatchLeave(out BlockContainer? blockContainer))
 			{
 				// success
-				return blockContainer;
+				return (blockContainer, caseBlockOrLeave);
 			}
 			else
 			{
-				return null;
+				return (null, caseBlockOrLeave);
 			}
 		}
 
@@ -1030,20 +1031,20 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			}
 
-			var stringValues = new List<(string Value, ILInstruction TargetBlockOrLeave)>();
+			var stringValues = new List<(string? Value, ILInstruction TargetBlockOrLeave)>();
 			SwitchSection defaultSection = switchInst.GetDefaultSection();
-			if (!(defaultSection.Body.MatchBranch(out Block exitOrDefaultBlock) || defaultSection.Body.MatchLeave(out _)))
+			if (!(defaultSection.Body.MatchBranch(out Block? exitOrDefaultBlock) || defaultSection.Body.MatchLeave(out _)))
 				return false;
 			foreach (var section in switchInst.Sections)
 			{
 				if (section == defaultSection)
 					continue;
 				// extract target block
-				if (!section.Body.MatchBranch(out Block target))
+				if (!section.Body.MatchBranch(out Block? target))
 					return false;
-				string stringValue;
+				string? stringValue;
 				bool emptyStringEqualsNull;
-				if (MatchRoslynEmptyStringCaseBlockHead(target, switchValueLoad.Variable, out ILInstruction targetOrLeave, out Block currentExitBlock))
+				if (MatchRoslynEmptyStringCaseBlockHead(target, switchValueLoad.Variable, out ILInstruction? targetOrLeave, out Block? currentExitBlock))
 				{
 					stringValue = "";
 					emptyStringEqualsNull = false;
@@ -1168,7 +1169,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			// implements https://github.com/dotnet/roslyn/pull/66081
 			// if (comp(ldloc switchValueVar == ldnull)) br nullCase
 			// br nextBlock
-			Block switchOnLengthBlock;
+			Block? switchOnLengthBlock;
 			int switchOnLengthBlockStartOffset;
 			Block? nullCase = null;
 			if (instructions[i].MatchIfInstruction(out var condition, out var exitBlockJump)
@@ -1206,7 +1207,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			Block? defaultCase = null;
 			if (!MatchSwitchOnLengthBlock(ref switchValueVar, switchOnLengthBlock, switchOnLengthBlockStartOffset, out var blocksByLength))
 				return false;
-			List<(string, ILInstruction)> stringValues = new();
+			List<(string?, ILInstruction)> stringValues = new();
 			foreach (var b in blocksByLength)
 			{
 				if (b.Length.Count() != 1)
@@ -1231,7 +1232,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							}
 						}
 					}
-					else if (MatchRoslynCaseBlockHead(b.TargetBlock, switchValueVar, out var bodyOrLeave, out var exit, out string stringValue, out _))
+					else if (MatchRoslynCaseBlockHead(b.TargetBlock, switchValueVar, out var bodyOrLeave, out var exit, out string? stringValue, out _))
 					{
 						if (exit != defaultCase)
 							return false;
@@ -1269,7 +1270,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 			context.Step(nameof(MatchRoslynSwitchOnStringUsingLengthAndChar), instructions[i]);
 			var defaultLabel = new LongSet(new LongInterval(0, stringValues.Count)).Invert();
-			var values = new string[stringValues.Count];
+			var values = new string?[stringValues.Count];
 			var sections = new SwitchSection[stringValues.Count];
 			foreach (var (idx, (value, bodyInstruction)) in stringValues.WithIndex())
 			{
@@ -1400,7 +1401,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return results?.Count > 0;
 			}
 
-			bool MatchSwitchOnLengthBlock(ref ILVariable switchValueVar, Block switchOnLengthBlock, int startOffset, [NotNullWhen(true)] out List<(LongSet Length, Block TargetBlock)>? blocks)
+			bool MatchSwitchOnLengthBlock(ref ILVariable? switchValueVar, Block switchOnLengthBlock, int startOffset, out List<(LongSet Length, Block TargetBlock)>? blocks)
 			{
 				blocks = null;
 				SwitchInstruction? @switch;
@@ -1476,6 +1477,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					default:
 						return false;
 				}
+
 				if (@switch == null)
 					return true;
 				blocks = new(@switch.Sections.Count);
@@ -1507,7 +1509,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		///	    br newDefaultBlock
 		/// }
 		/// </summary>
-		private bool IsNullCheckInDefaultBlock(ref Block exitOrDefaultBlock, ILVariable switchVar, [NotNullWhen(true)] out Block? nullValueCaseBlock)
+		private bool IsNullCheckInDefaultBlock(ref Block? exitOrDefaultBlock, ILVariable switchVar, [NotNullWhen(true)] out Block? nullValueCaseBlock)
 		{
 			nullValueCaseBlock = null;
 			if (exitOrDefaultBlock == null)
@@ -1533,7 +1535,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// if (call op_Equality(ldloc switchValueVar, stringValue)) br body
 		/// br exit
 		/// </summary>
-		bool MatchRoslynCaseBlockHead(Block target, ILVariable switchValueVar, [NotNullWhen(true)] out ILInstruction? bodyOrLeave, [NotNullWhen(true)] out Block? defaultOrExitBlock, [NotNullWhen(true)] out string? stringValue, out bool emptyStringEqualsNull)
+		bool MatchRoslynCaseBlockHead(Block target, ILVariable switchValueVar, [NotNullWhen(true)] out ILInstruction? bodyOrLeave, out Block? defaultOrExitBlock, out string? stringValue, out bool emptyStringEqualsNull)
 		{
 			bodyOrLeave = null;
 			defaultOrExitBlock = null;
@@ -1593,7 +1595,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		/// 	br exit
 		/// }
 		/// </summary>
-		bool MatchRoslynEmptyStringCaseBlockHead(Block target, ILVariable switchValueVar, [NotNullWhen(true)] out ILInstruction? bodyOrLeave, [NotNullWhen(true)] out Block? defaultOrExitBlock)
+		bool MatchRoslynEmptyStringCaseBlockHead(Block target, ILVariable switchValueVar, [NotNullWhen(true)] out ILInstruction? bodyOrLeave, out Block? defaultOrExitBlock)
 		{
 			bodyOrLeave = null;
 			defaultOrExitBlock = null;
@@ -1628,6 +1630,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (bodyBranch.MatchLeave(out _))
 			{
+
 				bodyOrLeave = bodyBranch;
 				return true;
 			}

ICSharpCode.Decompiler/Semantics/ConstantResolveResult.cs

@@ -32,9 +32,9 @@ namespace ICSharpCode.Decompiler.Semantics
 	/// </summary>
 	public class ConstantResolveResult : ResolveResult
 	{
-		object constantValue;
+		object? constantValue;
 
-		public ConstantResolveResult(IType type, object constantValue) : base(type)
+		public ConstantResolveResult(IType type, object? constantValue) : base(type)
 		{
 			this.constantValue = constantValue;
 		}
@@ -43,7 +43,7 @@ namespace ICSharpCode.Decompiler.Semantics
 			get { return true; }
 		}
 
-		public override object ConstantValue {
+		public override object? ConstantValue {
 			get { return constantValue; }
 		}
 

ICSharpCode.Decompiler/TypeSystem/ReflectionHelper.cs

@@ -227,7 +227,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// <summary>
 		/// Gets the type code for the specified type, or TypeCode.Empty if none of the other type codes match.
 		/// </summary>
-		public static TypeCode GetTypeCode(this IType type)
+		public static TypeCode GetTypeCode(this IType? type)
 		{
 			ITypeDefinition? def = type as ITypeDefinition;
 			if (def != null)

ICSharpCode.Decompiler/TypeSystem/TaskType.cs

@@ -74,8 +74,8 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				var arg = attribute.FixedArguments[0];
 				if (!arg.Type.IsKnownType(KnownTypeCode.Type))
 					return false;
-				builderType = (IType)arg.Value;
-				return true;
+				builderType = arg.Value as IType;
+				return builderType != null;
 			}
 			return false;
 		}

ILSpy.BamlDecompiler/BamlResourceNodeFactory.cs

@@ -35,7 +35,7 @@ namespace ILSpy.BamlDecompiler
 	[PartCreationPolicy(CreationPolicy.Shared)]
 	public sealed class BamlResourceNodeFactory : IResourceNodeFactory
 	{
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			if (resource.Name.EndsWith(".baml", StringComparison.OrdinalIgnoreCase))
 				return new BamlResourceEntryNode(resource.Name, resource.TryOpenStream);

ILSpy/Languages/ILAstLanguage.cs

@@ -39,9 +39,9 @@ namespace ICSharpCode.ILSpy
 	/// </summary>
 	abstract class ILAstLanguage : Language
 	{
-		public event EventHandler StepperUpdated;
+		public event EventHandler? StepperUpdated;
 
-		protected virtual void OnStepperUpdated(EventArgs e = null)
+		protected virtual void OnStepperUpdated(EventArgs? e = null)
 		{
 			StepperUpdated?.Invoke(this, e ?? new EventArgs());
 		}

ILSpy/MainWindow.xaml.cs

@@ -44,6 +44,7 @@ using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.TypeSystem.Implementation;
 using ICSharpCode.ILSpy.AppEnv;
 using ICSharpCode.ILSpy.Commands;
+using ICSharpCode.ILSpy.Controls.TreeView;
 using ICSharpCode.ILSpy.Docking;
 using ICSharpCode.ILSpy.Options;
 using ICSharpCode.ILSpy.Search;
@@ -51,16 +52,15 @@ using ICSharpCode.ILSpy.TextView;
 using ICSharpCode.ILSpy.Themes;
 using ICSharpCode.ILSpy.TreeNodes;
 using ICSharpCode.ILSpy.Updates;
+using ICSharpCode.ILSpy.Util;
 using ICSharpCode.ILSpy.ViewModels;
 using ICSharpCode.ILSpyX;
+using ICSharpCode.ILSpyX.Extensions;
 using ICSharpCode.ILSpyX.FileLoaders;
 using ICSharpCode.ILSpyX.Settings;
-using ICSharpCode.ILSpy.Controls.TreeView;
-using ICSharpCode.ILSpy.Util;
-using ICSharpCode.ILSpyX.Extensions;
+using ICSharpCode.ILSpyX.TreeView;
 
 using Microsoft.Win32;
-using ICSharpCode.ILSpyX.TreeView;
 
 using TomsToolbox.Composition;
 
@@ -749,10 +749,10 @@ namespace ICSharpCode.ILSpy
 			}
 		}
 
-		internal static IEntity FindEntityInRelevantAssemblies(string navigateTo, IEnumerable<LoadedAssembly> relevantAssemblies)
+		internal static IEntity? FindEntityInRelevantAssemblies(string navigateTo, IEnumerable<LoadedAssembly> relevantAssemblies)
 		{
-			ITypeReference typeRef = null;
-			IMemberReference memberRef = null;
+			ITypeReference? typeRef = null;
+			IMemberReference? memberRef = null;
 			if (navigateTo.StartsWith("T:", StringComparison.Ordinal))
 			{
 				typeRef = IdStringProvider.ParseTypeName(navigateTo);

ILSpy/TextView/DocumentationUIBuilder.cs

@@ -128,7 +128,7 @@ namespace ICSharpCode.ILSpy.TextView
 			AddBlock(block);
 		}
 
-		public void AddXmlDocumentation(string xmlDocumentation, IEntity declaringEntity, Func<string, IEntity> resolver)
+		public void AddXmlDocumentation(string xmlDocumentation, IEntity declaringEntity, Func<string, IEntity?> resolver)
 		{
 			if (xmlDocumentation == null)
 				return;

ILSpy/TreeNodes/ResourceNodes/CursorResourceEntryNode.cs

@@ -36,7 +36,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	{
 		static readonly string[] imageFileExtensions = { ".cur" };
 
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			string key = resource.Name;
 			foreach (string fileExt in imageFileExtensions)
@@ -70,7 +70,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 						return false;
 					//HACK: windows imaging does not understand that .cur files have the same layout as .ico
 					// so load to data, and modify the ResourceType in the header to make look like an icon...
-					MemoryStream s = data as MemoryStream;
+					MemoryStream? s = data as MemoryStream;
 					if (s == null)
 					{
 						// data was stored in another stream type (e.g. PinnedBufferedMemoryStream)

ILSpy/TreeNodes/ResourceNodes/IResourceNodeFactory.cs

@@ -26,6 +26,6 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	/// </summary>
 	public interface IResourceNodeFactory
 	{
-		ITreeNode CreateNode(Resource resource);
+		ITreeNode? CreateNode(Resource resource);
 	}
 }

ILSpy/TreeNodes/ResourceNodes/IconResourceEntryNode.cs

@@ -34,7 +34,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	[PartCreationPolicy(CreationPolicy.Shared)]
 	sealed class IconResourceNodeFactory : IResourceNodeFactory
 	{
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			if (resource.Name.EndsWith(".ico", StringComparison.OrdinalIgnoreCase))
 			{
@@ -46,7 +46,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 	sealed class IconResourceEntryNode : ResourceEntryNode
 	{
-		public IconResourceEntryNode(string key, Func<Stream> data)
+		public IconResourceEntryNode(string key, Func<Stream?> data)
 			: base(key, data)
 		{
 		}

ILSpy/TreeNodes/ResourceNodes/ImageListResourceEntryNode.cs

@@ -31,12 +31,12 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	[PartCreationPolicy(CreationPolicy.Shared)]
 	sealed class ImageListResourceEntryNodeFactory : IResourceNodeFactory
 	{
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			return null;
 		}
 
-		public ILSpyTreeNode CreateNode(string key, object data)
+		public ILSpyTreeNode? CreateNode(string key, object data)
 		{
 			if (data is ImageListStreamer)
 				return new ImageListResourceEntryNode(key, (ImageListStreamer)data);

ILSpy/TreeNodes/ResourceNodes/ImageResourceEntryNode.cs

@@ -36,7 +36,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	{
 		static readonly string[] imageFileExtensions = { ".png", ".gif", ".bmp", ".jpg" };
 
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			string key = resource.Name;
 			foreach (string fileExt in imageFileExtensions)
@@ -50,7 +50,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 	sealed class ImageResourceEntryNode : ResourceEntryNode
 	{
-		public ImageResourceEntryNode(string key, Func<Stream> openStream)
+		public ImageResourceEntryNode(string key, Func<Stream?> openStream)
 			: base(key, openStream)
 		{
 		}

ILSpy/TreeNodes/ResourceNodes/ResourceEntryNode.cs

@@ -34,18 +34,18 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	public class ResourceEntryNode : ILSpyTreeNode
 	{
 		private readonly string key;
-		private readonly Func<Stream> openStream;
+		private readonly Func<Stream?> openStream;
 
 		public override object Text => Language.EscapeName(key);
 
 		public override object Icon => Images.Resource;
 
-		protected Stream OpenStream()
+		protected Stream? OpenStream()
 		{
 			return openStream();
 		}
 
-		public ResourceEntryNode(string key, Func<Stream> openStream)
+		public ResourceEntryNode(string key, Func<Stream?> openStream)
 		{
 			if (key == null)
 				throw new ArgumentNullException(nameof(key));
@@ -57,7 +57,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		public static ILSpyTreeNode Create(Resource resource)
 		{
-			ILSpyTreeNode result = null;
+			ILSpyTreeNode? result = null;
 			foreach (var factory in App.ExportProvider.GetExportedValues<IResourceNodeFactory>())
 			{
 				result = factory.CreateNode(resource) as ILSpyTreeNode;
@@ -78,13 +78,14 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			language.WriteCommentLine(output, string.Format("{0} = {1}", key, data));
 		}
 
-		public override bool Save(ViewModels.TabPageModel tabPage)
+		public override bool Save(ViewModels.TabPageModel? tabPage)
 		{
 			SaveFileDialog dlg = new SaveFileDialog();
 			dlg.FileName = Path.GetFileName(WholeProjectDecompiler.SanitizeFileName(key));
 			if (dlg.ShowDialog() == true)
 			{
 				using var data = OpenStream();
+
 				using var fs = dlg.OpenFile();
 				data.CopyTo(fs);
 			}

ILSpy/TreeNodes/ResourceNodes/ResourcesFileTreeNode.cs

@@ -41,7 +41,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 	[PartCreationPolicy(CreationPolicy.Shared)]
 	sealed class ResourcesFileTreeNodeFactory : IResourceNodeFactory
 	{
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			if (resource.Name.EndsWith(".resources", StringComparison.OrdinalIgnoreCase))
 			{
@@ -50,7 +50,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			return null;
 		}
 
-		public ILSpyTreeNode CreateNode(string key, object data)
+		public ILSpyTreeNode? CreateNode(string key, object data)
 		{
 			return null;
 		}

ILSpy/TreeNodes/ResourceNodes/XamlResourceNode.cs

@@ -34,7 +34,7 @@ namespace ICSharpCode.ILSpy.Xaml
 	[PartCreationPolicy(CreationPolicy.Shared)]
 	sealed class XamlResourceNodeFactory : IResourceNodeFactory
 	{
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			if (resource.Name.EndsWith(".xaml", StringComparison.OrdinalIgnoreCase))
 				return new XamlResourceEntryNode(resource.Name, resource.TryOpenStream);
@@ -45,9 +45,9 @@ namespace ICSharpCode.ILSpy.Xaml
 
 	sealed class XamlResourceEntryNode : ResourceEntryNode
 	{
-		string xaml;
+		string? xaml;
 
-		public XamlResourceEntryNode(string key, Func<Stream> openStream) : base(key, openStream)
+		public XamlResourceEntryNode(string key, Func<Stream?> openStream) : base(key, openStream)
 		{
 		}
 

ILSpy/TreeNodes/ResourceNodes/XmlResourceNode.cs

@@ -36,7 +36,7 @@ namespace ICSharpCode.ILSpy.Xaml
 	{
 		private readonly static string[] xmlFileExtensions = { ".xml", ".xsd", ".xslt" };
 
-		public ITreeNode CreateNode(Resource resource)
+		public ITreeNode? CreateNode(Resource resource)
 		{
 			string key = resource.Name;
 			foreach (string fileExt in xmlFileExtensions)
@@ -50,9 +50,9 @@ namespace ICSharpCode.ILSpy.Xaml
 
 	sealed class XmlResourceEntryNode : ResourceEntryNode
 	{
-		string xml;
+		string? xml;
 
-		public XmlResourceEntryNode(string key, Func<Stream> data)
+		public XmlResourceEntryNode(string key, Func<Stream?> data)
 			: base(key, data)
 		{
 		}
@@ -74,7 +74,7 @@ namespace ICSharpCode.ILSpy.Xaml
 		public override bool View(TabPageModel tabPage)
 		{
 			AvalonEditTextOutput output = new AvalonEditTextOutput();
-			IHighlightingDefinition highlighting = null;
+			IHighlightingDefinition? highlighting = null;
 
 			tabPage.ShowTextView(textView => textView.RunWithCancellation(
 				token => Task.Factory.StartNew(

ILSpy/Views/DebugSteps.xaml.cs

@@ -48,7 +48,7 @@ namespace ICSharpCode.ILSpy
 #endif
 		}
 
-		private void WritingOptions_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
+		private void WritingOptions_PropertyChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
 		{
 			DecompileAsync(lastSelectedStep);
 		}
@@ -80,7 +80,7 @@ namespace ICSharpCode.ILSpy
 #endif
 		}
 
-		private void ILAstStepperUpdated(object sender, EventArgs e)
+		private void ILAstStepperUpdated(object? sender, EventArgs? e)
 		{
 #if DEBUG
 			if (language == null)