applied fixer for drect assignment from null

.editorconfig

@@ -147,3 +147,6 @@ dotnet_naming_rule.private_fields_rule.symbols = private_fields_symbols
 
 # MEF006: No importing constructor
 dotnet_diagnostic.MEF006.severity = silent
+
+
+dotnet_diagnostic.IDE2003.severity = silent

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -406,7 +406,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		static readonly Regex automaticPropertyBackingFieldRegex = new Regex(@"^<(.*)>k__BackingField$",
 			RegexOptions.Compiled | RegexOptions.CultureInvariant);
 
-		static bool IsAutomaticPropertyBackingField(FieldDefinition field, MetadataReader metadata, out string propertyName)
+		static bool IsAutomaticPropertyBackingField(FieldDefinition field, MetadataReader metadata, out string? propertyName)
 		{
 			propertyName = null;
 			var name = metadata.GetString(field.Name);
@@ -631,8 +631,8 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		void DoDecompileTypes(IEnumerable<TypeDefinitionHandle> types, DecompileRun decompileRun, ITypeResolveContext decompilationContext, SyntaxTree syntaxTree)
 		{
-			string currentNamespace = null;
-			AstNode groupNode = null;
+			string? currentNamespace = null;
+			AstNode? groupNode = null;
 			foreach (var typeDefHandle in types)
 			{
 				var typeDef = module.GetDefinition(typeDefHandle);
@@ -1027,7 +1027,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 
 			bool first = true;
-			ITypeDefinition parentTypeDef = null;
+			ITypeDefinition? parentTypeDef = null;
 
 			foreach (var entity in definitions)
 			{
@@ -1315,7 +1315,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					TypeKind.Struct => (settings.RecordStructs && typeDef.IsRecord) || settings.UsePrimaryConstructorSyntaxForNonRecordTypes,
 					_ => false,
 				};
-				RecordDecompiler recordDecompiler = isRecordLike ? new RecordDecompiler(typeSystem, typeDef, settings, CancellationToken) : null;
+				RecordDecompiler? recordDecompiler = isRecordLike ? new RecordDecompiler(typeSystem, typeDef, settings, CancellationToken) : null;
 				if (recordDecompiler != null)
 					decompileRun.RecordDecompilers.Add(typeDef, recordDecompiler);
 
@@ -1779,7 +1779,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					);
 					body = statementBuilder.ConvertAsBlock(function.Body);
 
-					Comment prev = null;
+					Comment? prev = null;
 					foreach (string warning in function.Warnings)
 					{
 						body.InsertChildAfter(prev, prev = new Comment(warning), Roles.Comment);
@@ -1916,7 +1916,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return found;
 		}
 
-		bool FindAttribute(EntityDeclaration entityDecl, KnownAttribute attributeType, out Syntax.Attribute attribute)
+		bool FindAttribute(EntityDeclaration entityDecl, KnownAttribute attributeType, out Syntax.Attribute? attribute)
 		{
 			attribute = null;
 			foreach (var section in entityDecl.Attributes)
@@ -2016,7 +2016,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		internal static bool IsFixedField(IField field, out IType type, out int elementCount)
+		internal static bool IsFixedField(IField field, out IType? type, out int elementCount)
 		{
 			type = null;
 			elementCount = 0;

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Text;
 
@@ -47,7 +48,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			public TranslatedExpression[] Arguments;
 			public IParameter[] ExpectedParameters;
 			public string[] ParameterNames;
-			public string[] ArgumentNames;
+			public string[]? ArgumentNames;
 			public int FirstOptionalArgumentIndex;
 			public BitSet IsPrimitiveValue;
 			public IReadOnlyList<int> ArgumentToParameterMap;
@@ -146,7 +147,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				for (int i = 0; i < Arguments.Length; i++)
 				{
-					string inferredName;
+					string? inferredName;
 					switch (Arguments[i].Expression)
 					{
 						case IdentifierExpression identifier:
@@ -188,13 +189,13 @@ namespace ICSharpCode.Decompiler.CSharp
 			this.typeSystem = typeSystem;
 		}
 
-		public TranslatedExpression Build(CallInstruction inst, IType typeHint = null)
+		public TranslatedExpression Build(CallInstruction inst, IType? typeHint = null)
 		{
 			if (inst is NewObj newobj && IL.Transforms.DelegateConstruction.MatchDelegateConstruction(newobj, out _, out _, out _))
 			{
 				return HandleDelegateConstruction(newobj);
 			}
-			if (settings.TupleTypes && TupleTransform.MatchTupleConstruction(inst as NewObj, out var tupleElements) && tupleElements.Length >= 2)
+			if (settings.TupleTypes && TupleTransform.MatchTupleConstruction(inst as NewObj, out var tupleElements) && tupleElements?.Length >= 2)
 			{
 				var elementTypes = TupleType.GetTupleElementTypes(inst.Method.DeclaringType);
 				var elementNames = typeHint is TupleType tt ? tt.ElementNames : default;
@@ -247,7 +248,8 @@ namespace ICSharpCode.Decompiler.CSharp
 			return result;
 		}
 
-		static bool IsSpanBasedStringConcat(CallInstruction call, out List<(ILInstruction, KnownTypeCode)> operands)
+
+		static bool IsSpanBasedStringConcat(CallInstruction call, [NotNullWhen(true)] out List<(ILInstruction, KnownTypeCode)>? operands)
 		{
 			operands = null;
 
@@ -313,8 +315,8 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		public ExpressionWithResolveResult Build(OpCode callOpCode, IMethod method,
 			IReadOnlyList<ILInstruction> callArguments,
-			IReadOnlyList<int> argumentToParameterMap = null,
-			IType constrainedTo = null)
+			IReadOnlyList<int>? argumentToParameterMap = null,
+			IType? constrainedTo = null)
 		{
 			if (method.IsExplicitInterfaceImplementation && callOpCode == OpCode.Call)
 			{
@@ -332,7 +334,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			var expectedTargetDetails = new ExpectedTargetDetails {
 				CallOpCode = callOpCode
 			};
-			ILFunction localFunction = null;
+			ILFunction? localFunction = null;
 			if (method.IsLocalFunction)
 			{
 				localFunction = expressionBuilder.ResolveLocalFunction(method);
@@ -523,7 +525,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		private ExpressionWithResolveResult HandleStringInterpolation(IMethod method, ArgumentList argumentList)
 		{
-			if (!TryGetStringInterpolationTokens(argumentList, out string format, out var tokens))
+			if (!TryGetStringInterpolationTokens(argumentList, out string? format, out var tokens))
 				return default;
 
 			var arguments = argumentList.Arguments;
@@ -543,7 +545,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				argument = new TranslatedExpression(element, arrayCreationRR.InitializerElements.First());
 			}
 
-			if (tokens.Count == 0)
+			if (tokens == null || tokens.Count == 0)
 			{
 				return default;
 			}
@@ -655,7 +657,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		}
 
 		public ExpressionWithResolveResult BuildDictionaryInitializerExpression(OpCode callOpCode, IMethod method,
-			InitializedObjectResolveResult target, IReadOnlyList<ILInstruction> indices, ILInstruction value = null)
+			InitializedObjectResolveResult target, IReadOnlyList<ILInstruction> indices, ILInstruction? value = null)
 		{
 			if (method is null)
 				throw new ArgumentNullException(nameof(method));
@@ -696,7 +698,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			);
 		}
 
-		private bool TryGetStringInterpolationTokens(ArgumentList argumentList, out string format, out List<(TokenKind Kind, int Index, int Alignment, string Format)> tokens)
+		private bool TryGetStringInterpolationTokens(ArgumentList argumentList, out string? format, out List<(TokenKind Kind, int Index, int Alignment, string? Format)>? tokens)
 		{
 			tokens = null;
 			format = null;
@@ -707,7 +709,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				return false;
 			if (!arguments.Skip(1).All(a => !a.Expression.DescendantsAndSelf.OfType<PrimitiveExpression>().Any(p => p.Value is string)))
 				return false;
-			tokens = new List<(TokenKind Kind, int Index, int Alignment, string Format)>();
+			tokens = new List<(TokenKind Kind, int Index, int Alignment, string? Format)>();
 			int i = 0;
 			format = (string)crr.ConstantValue;
 			foreach (var (kind, data) in TokenizeFormatString(format))
@@ -867,14 +869,14 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		private ArgumentList BuildArgumentList(ExpectedTargetDetails expectedTargetDetails, ResolveResult target, IMethod method,
-			int firstParamIndex, IReadOnlyList<ILInstruction> callArguments, IReadOnlyList<int> argumentToParameterMap)
+		private ArgumentList BuildArgumentList(ExpectedTargetDetails expectedTargetDetails, ResolveResult? target, IMethod method,
+			int firstParamIndex, IReadOnlyList<ILInstruction> callArguments, IReadOnlyList<int>? argumentToParameterMap)
 		{
 			ArgumentList list = new ArgumentList();
 
 			// Translate arguments to the expected parameter types
 			var arguments = new List<TranslatedExpression>(method.Parameters.Count);
-			string[] argumentNames = null;
+			string[]? argumentNames = null;
 			Debug.Assert(callArguments.Count == firstParamIndex + method.Parameters.Count);
 			var expectedParameters = new List<IParameter>(method.Parameters.Count); // parameters, but in argument order
 			bool isExpandedForm = false;
@@ -978,11 +980,11 @@ namespace ICSharpCode.Decompiler.CSharp
 			return p.Type.IsKnownType(KnownTypeCode.Boolean);
 		}
 
-		private bool TransformParamsArgument(ExpectedTargetDetails expectedTargetDetails, ResolveResult targetResolveResult,
+		private bool TransformParamsArgument(ExpectedTargetDetails expectedTargetDetails, ResolveResult? targetResolveResult,
 			IMethod method, IParameter parameter, TranslatedExpression arg, ref List<IParameter> expectedParameters,
 			ref List<TranslatedExpression> arguments)
 		{
-			if (CheckArgument(out int length, out IType elementType))
+			if (CheckArgument(out int length, out IType? elementType))
 			{
 				var expandedParameters = new List<IParameter>(expectedParameters);
 				var expandedArguments = new List<TranslatedExpression>(arguments);
@@ -1010,7 +1012,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			return false;
 
-			bool CheckArgument(out int len, out IType t)
+			bool CheckArgument(out int len, [NotNullWhen(true)] out IType? t)
 			{
 				len = 0;
 				t = null;
@@ -1069,7 +1071,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 			// initialize requireTarget flag
 			bool requireTarget;
-			ResolveResult targetResolveResult;
+			ResolveResult? targetResolveResult;
 			if ((allowedTransforms & CallTransformation.RequireTarget) != 0)
 			{
 				if (settings.AlwaysQualifyMemberReferences || expressionBuilder.HidesVariableWithName(method.Name))
@@ -1394,8 +1396,8 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		OverloadResolutionErrors IsUnambiguousCall(ExpectedTargetDetails expectedTargetDetails, IMethod method,
 			ResolveResult target, IType[] typeArguments, ResolveResult[] arguments,
-			string[] argumentNames, int firstOptionalArgumentIndex,
-			out IParameterizedMember foundMember, out bool bestCandidateIsExpandedForm)
+			string[]? argumentNames, int firstOptionalArgumentIndex,
+			out IParameterizedMember? foundMember, out bool bestCandidateIsExpandedForm)
 		{
 			foundMember = null;
 			bestCandidateIsExpandedForm = false;
@@ -1504,7 +1506,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		}
 
 		bool IsUnambiguousAccess(ExpectedTargetDetails expectedTargetDetails, ResolveResult target, IMethod method,
-			IList<TranslatedExpression> arguments, string[] argumentNames, out IMember foundMember)
+			IList<TranslatedExpression> arguments, string[] argumentNames, out IMember? foundMember)
 		{
 			Log.WriteLine("IsUnambiguousAccess: Performing overload resolution for " + method);
 			Log.WriteCollection("  Arguments: ", arguments.Select(a => a.ResolveResult));
@@ -1551,7 +1553,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		}
 
 		ExpressionWithResolveResult HandleAccessorCall(ExpectedTargetDetails expectedTargetDetails, IMethod method,
-			TranslatedExpression target, List<TranslatedExpression> arguments, string[] argumentNames)
+			TranslatedExpression target, List<TranslatedExpression> arguments, string[]? argumentNames)
 		{
 			bool requireTarget;
 			if (settings.AlwaysQualifyMemberReferences || method.AccessorOwner.SymbolKind == SymbolKind.Indexer || expressionBuilder.HidesVariableWithName(method.AccessorOwner.Name))
@@ -1715,7 +1717,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					CastArguments(argumentList.Arguments, argumentList.ExpectedParameters);
 					break; // make sure that we don't not end up in an infinite loop
 				}
-				IType returnTypeOverride = null;
+				IType? returnTypeOverride = null;
 				if (typeSystem.MainModule.TypeSystemOptions.HasFlag(TypeSystemOptions.NativeIntegersWithoutAttribute))
 				{
 					// For DeclaringType, we don't use nint/nuint (so that DeclaringType.GetConstructors etc. works),
@@ -1932,7 +1934,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				bool targetCasted = false;
 				bool addTypeArguments = false;
 				// Initial inputs for IsUnambiguousMethodReference:
-				ResolveResult targetResolveResult = targetAdded ? target.ResolveResult : null;
+				ResolveResult? targetResolveResult = targetAdded ? target.ResolveResult : null;
 				IReadOnlyList<IType> typeArguments = EmptyList<IType>.Instance;
 				// Find somewhat minimal solution:
 				ResolveResult result;

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -153,7 +153,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		public TranslatedExpression Translate(ILInstruction inst, IType typeHint = null)
+		public TranslatedExpression Translate(ILInstruction inst, IType? typeHint = null)
 		{
 			Debug.Assert(inst != null);
 			cancellationToken.ThrowIfCancellationRequested();
@@ -289,7 +289,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return !(target.Expression is ThisReferenceExpression || target.Expression is BaseReferenceExpression);
 		}
 
-		ExpressionWithResolveResult ConvertField(IField field, ILInstruction targetInstruction = null)
+		ExpressionWithResolveResult ConvertField(IField field, ILInstruction? targetInstruction = null)
 		{
 			var target = TranslateTarget(targetInstruction,
 				nonVirtualInvocation: true,
@@ -328,7 +328,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				return result == null || result.IsError || !result.Member.Equals(field, NormalizeTypeVisitor.TypeErasure);
 			}
 
-			MemberResolveResult mrr;
+			MemberResolveResult? mrr;
 			while (IsAmbiguousAccess(out mrr))
 			{
 				if (!requireTarget)
@@ -486,7 +486,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		StackAllocExpression TranslateLocAlloc(LocAlloc inst, IType typeHint, out IType elementType)
 		{
 			TranslatedExpression countExpression;
-			PointerType pointerType;
+			PointerType? pointerType;
 			if (inst.Argument.MatchBinaryNumericInstruction(BinaryNumericOperator.Mul, out var left, out var right)
 				&& right.UnwrapConv(ConversionKind.SignExtend).UnwrapConv(ConversionKind.ZeroExtend).MatchSizeOf(out elementType))
 			{
@@ -638,7 +638,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Expression expr;
 			IType constantType;
-			object constantValue;
+			object? constantValue;
 			if (type.IsReferenceType == true || type.IsKnownType(KnownTypeCode.NullableOfT))
 			{
 				expr = new NullReferenceExpression();
@@ -960,7 +960,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					.WithILInstruction(inst);
 			}
 
-			OperatorResolveResult rr = resolver.ResolveBinaryOperator(inst.Kind.ToBinaryOperatorType(), left.ResolveResult, right.ResolveResult) as OperatorResolveResult;
+			OperatorResolveResult? rr = resolver.ResolveBinaryOperator(inst.Kind.ToBinaryOperatorType(), left.ResolveResult, right.ResolveResult) as OperatorResolveResult;
 			if (rr == null || rr.IsError || rr.UserDefinedOperatorMethod != null
 				|| NullableType.GetUnderlyingType(rr.Operands[0].Type).GetStackType() != inst.InputType
 				|| !rr.Type.IsKnownType(KnownTypeCode.Boolean))
@@ -1387,7 +1387,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		internal TranslatedExpression CallUnsafeIntrinsic(string name, Expression[] arguments, IType returnType, ILInstruction inst = null, IEnumerable<IType> typeArguments = null)
+		internal TranslatedExpression CallUnsafeIntrinsic(string name, Expression[] arguments, IType returnType, ILInstruction? inst = null, IEnumerable<IType>? typeArguments = null)
 		{
 			var target = new MemberReferenceExpression {
 				Target = new TypeReferenceExpression(astBuilder.ConvertType(compilation.FindType(KnownTypeCode.Unsafe))),
@@ -1458,7 +1458,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (sub.CheckForOverflow)
 				return null;
 			// First, attempt to parse the 'sizeof' on the RHS
-			IType elementType;
+			IType? elementType;
 			if (inst.Right.MatchLdcI(out long elementSize))
 			{
 				elementType = null;
@@ -2397,7 +2397,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			);
 			var body = builder.ConvertAsBlock(function.Body);
 
-			Comment prev = null;
+			Comment? prev = null;
 			foreach (string warning in function.Warnings)
 			{
 				body.InsertChildAfter(prev, prev = new Comment(warning), Roles.Comment);
@@ -2612,7 +2612,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		internal TranslatedExpression TranslateTarget(ILInstruction target, bool nonVirtualInvocation,
+		internal TranslatedExpression TranslateTarget(ILInstruction? target, bool nonVirtualInvocation,
 			bool memberStatic, IType memberDeclaringType)
 		{
 			// If references are missing member.IsStatic might not be set correctly.
@@ -3393,7 +3393,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			var elementsStack = new Stack<List<TranslatedExpression>>();
 			var elements = new List<TranslatedExpression>(block.Instructions.Count);
 			elementsStack.Push(elements);
-			List<IL.Transforms.AccessPathElement> currentPath = null;
+			List<IL.Transforms.AccessPathElement>? currentPath = null;
 			var indexVariables = new Dictionary<ILVariable, ILInstruction>();
 			foreach (var inst in block.Instructions.Skip(1))
 			{
@@ -3602,7 +3602,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 			}
 			ArraySpecifier[] additionalSpecifiers;
-			AstType typeExpression;
+			AstType? typeExpression;
 			if (settings.AnonymousTypes && type.ContainsAnonymousType())
 			{
 				typeExpression = null;
@@ -4023,7 +4023,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		protected internal override TranslatedExpression VisitAwait(Await inst, TranslationContext context)
 		{
-			IType expectedType = null;
+			IType? expectedType = null;
 			if (inst.GetAwaiterMethod != null)
 			{
 				if (inst.GetAwaiterMethod.IsStatic)

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpAmbience.cs

@@ -58,7 +58,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			TypeSystemAstBuilder astBuilder = CreateAstBuilder();
 			AstNode node = astBuilder.ConvertSymbol(symbol);
 			writer.StartNode(node);
-			EntityDeclaration entityDecl = node as EntityDeclaration;
+			EntityDeclaration? entityDecl = node as EntityDeclaration;
 			if (entityDecl != null)
 				PrintModifiers(entityDecl.Modifiers, writer);
 

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -200,7 +200,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			WriteKeyword(tokenRole.Token, tokenRole);
 		}
 
-		protected virtual void WriteKeyword(string token, Role tokenRole = null)
+		protected virtual void WriteKeyword(string token, Role? tokenRole = null)
 		{
 			writer.WriteKeyword(tokenRole, token);
 			isAtStartOfLine = false;
@@ -529,7 +529,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				NewLine();
 				return;
 			}
-			BlockStatement block = embeddedStatement as BlockStatement;
+			BlockStatement? block = embeddedStatement as BlockStatement;
 			if (block != null)
 			{
 				WriteBlock(block, policy.StatementBraceStyle);
@@ -672,7 +672,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		{
 			// "int a; new List<int> { a = 1 };" is an object initalizers and invalid, but
 			// "int a; new List<int> { { a = 1 } };" is a valid collection initializer.
-			AssignmentExpression ae = expr as AssignmentExpression;
+			AssignmentExpression? ae = expr as AssignmentExpression;
 			return ae != null && ae.Operator == AssignmentOperatorType.Assign;
 		}
 
@@ -703,7 +703,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			OpenBrace(wrap ? policy.ArrayInitializerBraceStyle : BraceStyle.EndOfLine, newLine: wrap);
 			if (!wrap)
 				Space();
-			AstNode last = null;
+			AstNode? last = null;
 			foreach (var (idx, node) in elements.WithIndex())
 			{
 				if (idx > 0)
@@ -1658,7 +1658,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				if (typeDeclaration.ClassType == ClassType.Enum)
 				{
 					bool first = true;
-					AstNode last = null;
+					AstNode? last = null;
 					foreach (var member in typeDeclaration.Members)
 					{
 						if (first)
@@ -2340,7 +2340,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			StartNode(constructorDeclaration);
 			WriteAttributes(constructorDeclaration.Attributes);
 			WriteModifiers(constructorDeclaration.ModifierTokens);
-			TypeDeclaration type = constructorDeclaration.Parent as TypeDeclaration;
+			TypeDeclaration? type = constructorDeclaration.Parent as TypeDeclaration;
 			if (type != null && type.Name != constructorDeclaration.Name)
 				WriteIdentifier((Identifier)type.NameToken.Clone());
 			else
@@ -2386,7 +2386,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				Space();
 			}
 			WriteToken(DestructorDeclaration.TildeRole);
-			TypeDeclaration type = destructorDeclaration.Parent as TypeDeclaration;
+			TypeDeclaration? type = destructorDeclaration.Parent as TypeDeclaration;
 			if (type != null && type.Name != destructorDeclaration.Name)
 				WriteIdentifier((Identifier)type.NameToken.Clone());
 			else
@@ -2949,7 +2949,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 
 		public virtual void VisitCSharpTokenNode(CSharpTokenNode cSharpTokenNode)
 		{
-			CSharpModifierToken mod = cSharpTokenNode as CSharpModifierToken;
+			CSharpModifierToken? mod = cSharpTokenNode as CSharpModifierToken;
 			if (mod != null)
 			{
 				// ITokenWriter assumes that each node processed between a

ICSharpCode.Decompiler/CSharp/OutputVisitor/InsertMissingTokensDecorator.cs

@@ -105,20 +105,20 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public override void WriteKeyword(Role role, string keyword)
 		{
 			TextLocation start = locationProvider.Location;
-			CSharpTokenNode t = null;
+			CSharpTokenNode? t = null;
 			if (role is TokenRole)
 				t = new CSharpTokenNode(start, (TokenRole)role);
 			else if (role == EntityDeclaration.ModifierRole)
 				t = new CSharpModifierToken(start, CSharpModifierToken.GetModifierValue(keyword));
 			else if (keyword == "this")
 			{
-				ThisReferenceExpression node = nodes.Peek().LastOrDefault() as ThisReferenceExpression;
+				ThisReferenceExpression? node = nodes.Peek().LastOrDefault() as ThisReferenceExpression;
 				if (node != null)
 					node.Location = start;
 			}
 			else if (keyword == "base")
 			{
-				BaseReferenceExpression node = nodes.Peek().LastOrDefault() as BaseReferenceExpression;
+				BaseReferenceExpression? node = nodes.Peek().LastOrDefault() as BaseReferenceExpression;
 				if (node != null)
 					node.Location = start;
 			}
@@ -140,7 +140,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 
 		public override void WritePrimitiveValue(object value, LiteralFormat format = LiteralFormat.None)
 		{
-			Expression node = nodes.Peek().LastOrDefault() as Expression;
+			Expression? node = nodes.Peek().LastOrDefault() as Expression;
 			var startLocation = locationProvider.Location;
 			base.WritePrimitiveValue(value, format);
 			if (node is PrimitiveExpression)
@@ -155,7 +155,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 
 		public override void WritePrimitiveType(string type)
 		{
-			PrimitiveType node = nodes.Peek().LastOrDefault() as PrimitiveType;
+			PrimitiveType? node = nodes.Peek().LastOrDefault() as PrimitiveType;
 			if (node != null)
 				node.SetStartLocation(locationProvider.Location);
 			base.WritePrimitiveType(type);

ICSharpCode.Decompiler/CSharp/OutputVisitor/InsertParenthesesVisitor.cs

@@ -218,7 +218,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public override void VisitUnaryOperatorExpression(UnaryOperatorExpression unaryOperatorExpression)
 		{
 			ParenthesizeIfRequired(unaryOperatorExpression.Expression, GetPrecedence(unaryOperatorExpression));
-			UnaryOperatorExpression child = unaryOperatorExpression.Expression as UnaryOperatorExpression;
+			UnaryOperatorExpression? child = unaryOperatorExpression.Expression as UnaryOperatorExpression;
 			if (child != null && InsertParenthesesForReadability)
 				Parenthesize(child);
 			base.VisitUnaryOperatorExpression(unaryOperatorExpression);
@@ -233,7 +233,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			}
 			// There's a nasty issue in the C# grammar: cast expressions including certain operators are ambiguous in some cases
 			// "(int)-1" is fine, but "(A)-b" is not a cast.
-			UnaryOperatorExpression uoe = castExpression.Expression as UnaryOperatorExpression;
+			UnaryOperatorExpression? uoe = castExpression.Expression as UnaryOperatorExpression;
 			if (uoe != null && !(uoe.Operator == UnaryOperatorType.BitNot || uoe.Operator == UnaryOperatorType.Not))
 			{
 				if (TypeCanBeMisinterpretedAsExpression(castExpression.Type))
@@ -242,7 +242,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				}
 			}
 			// The above issue can also happen with PrimitiveExpressions representing negative values:
-			PrimitiveExpression pe = castExpression.Expression as PrimitiveExpression;
+			PrimitiveExpression? pe = castExpression.Expression as PrimitiveExpression;
 			if (pe != null && pe.Value != null && TypeCanBeMisinterpretedAsExpression(castExpression.Type))
 			{
 				TypeCode typeCode = Type.GetTypeCode(pe.Value.GetType());
@@ -286,7 +286,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			// SimpleTypes can always be misinterpreted as IdentifierExpressions
 			// MemberTypes can be misinterpreted as MemberReferenceExpressions if they don't use double colon
 			// PrimitiveTypes or ComposedTypes can never be misinterpreted as expressions.
-			MemberType mt = type as MemberType;
+			MemberType? mt = type as MemberType;
 			if (mt != null)
 				return !mt.IsDoubleColon;
 			else
@@ -354,7 +354,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 
 		BinaryOperatorType? GetBinaryOperatorType(Expression expr)
 		{
-			BinaryOperatorExpression boe = expr as BinaryOperatorExpression;
+			BinaryOperatorExpression? boe = expr as BinaryOperatorExpression;
 			if (boe != null)
 				return boe.Operator;
 			else

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/TargetServices.cs

@@ -66,8 +66,8 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 					break;
 			}
 
-			string targetFrameworkIdentifier = null;
-			string targetFrameworkProfile = null;
+			string? targetFrameworkIdentifier = null;
+			string? targetFrameworkProfile = null;
 
 			string targetFramework = module.DetectTargetFrameworkId();
 			if (!string.IsNullOrEmpty(targetFramework))
@@ -245,7 +245,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 					break;
 				}
 
-				MetadataFile resolvedReference;
+				MetadataFile? resolvedReference;
 				try
 				{
 					resolvedReference = assemblyResolver.Resolve(reference);

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs

@@ -636,7 +636,7 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 			if (pos > 0)
 				text = text.Substring(0, pos);
 			text = text.Trim();
-			string extension = null;
+			string? extension = null;
 			int currentSegmentLength = 0;
 			if (treatAsFileName)
 			{
@@ -781,9 +781,9 @@ namespace ICSharpCode.Decompiler.CSharp.ProjectDecompiler
 
 	public record struct ProjectItemInfo(string ItemType, string FileName)
 	{
-		public List<PartialTypeInfo> PartialTypes { get; set; } = null;
+		public List<PartialTypeInfo>? PartialTypes { get; set; } = null;
 
-		public Dictionary<string, string> AdditionalProperties { get; set; } = null;
+		public Dictionary<string, string>? AdditionalProperties { get; set; } = null;
 
 		public ProjectItemInfo With(string name, string value)
 		{

ICSharpCode.Decompiler/CSharp/RecordDecompiler.cs

@@ -75,7 +75,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 			}
 
-			bool IsAutoProperty(IProperty p, out IField field)
+			bool IsAutoProperty(IProperty p, out IField? field)
 			{
 				field = null;
 				if (p.IsStatic)
@@ -108,7 +108,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				return field.Name == $"<{p.Name}>k__BackingField";
 			}
 
-			bool IsAutoGetter(IMethod method, out IField field)
+			bool IsAutoGetter(IMethod method, out IField? field)
 			{
 				field = null;
 				var body = DecompileBody(method);
@@ -129,7 +129,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 			}
 
-			bool IsAutoSetter(IMethod method, out IField field)
+			bool IsAutoSetter(IMethod method, out IField? field)
 			{
 				field = null;
 				Debug.Assert(!method.IsStatic);
@@ -672,7 +672,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				return true;
 			}
 
-			bool MatchStringBuilderAppendConstant(out string text)
+			bool MatchStringBuilderAppendConstant(out string? text)
 			{
 				text = null;
 				while (MatchStringBuilderAppend(body.Instructions[pos], builder, out var val) && val.MatchLdStr(out string valText))
@@ -684,7 +684,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		private bool MatchStringBuilderAppend(ILInstruction inst, ILVariable sb, out ILInstruction val)
+		private bool MatchStringBuilderAppend(ILInstruction inst, ILVariable sb, out ILInstruction? val)
 		{
 			val = null;
 			if (!(inst is CallVirt { Method: { Name: "Append", DeclaringType: { Namespace: "System.Text", Name: "StringBuilder" } } } call))
@@ -912,7 +912,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 		}
 
-		private bool MatchGetEqualityContract(ILInstruction inst, out ILInstruction target)
+		private bool MatchGetEqualityContract(ILInstruction inst, out ILInstruction? target)
 		{
 			target = null;
 			if (!(inst is CallInstruction { Method: { Name: "get_EqualityContract" } } call))
@@ -1099,7 +1099,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return returnInst != null && returnInst.MatchReturn(out var retVal) && retVal.MatchNop();
 		}
 
-		bool MatchMemberAccess(ILInstruction inst, out ILInstruction target, out IMember member)
+		bool MatchMemberAccess(ILInstruction inst, out ILInstruction? target, out IMember? member)
 		{
 			target = null;
 			member = null;

ICSharpCode.Decompiler/CSharp/RequiredNamespaceCollector.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			collector.CollectNamespaces(entity, module);
 		}
 
-		void CollectNamespaces(IEntity entity, MetadataModule module, CodeMappingInfo mappingInfo = null)
+		void CollectNamespaces(IEntity entity, MetadataModule module, CodeMappingInfo? mappingInfo = null)
 		{
 			if (entity == null || entity.MetadataToken.IsNil || module.MetadataFile is not MetadataFile corFile)
 				return;
@@ -334,7 +334,7 @@ namespace ICSharpCode.Decompiler.CSharp
 							case HandleKind.MethodDefinition:
 							case HandleKind.MethodSpecification:
 							case HandleKind.MemberReference:
-								IMember member;
+								IMember? member;
 								try
 								{
 									member = module.ResolveEntity(handle, genericContext) as IMember;

ICSharpCode.Decompiler/CSharp/Resolver/CSharpConversions.cs

@@ -523,10 +523,10 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			if (!(fromType.IsReferenceType == true && toType.IsReferenceType != false))
 				return false;
 
-			ArrayType fromArray = fromType as ArrayType;
+			ArrayType? fromArray = fromType as ArrayType;
 			if (fromArray != null)
 			{
-				ArrayType toArray = toType as ArrayType;
+				ArrayType? toArray = toType as ArrayType;
 				if (toArray != null)
 				{
 					// array covariance (the broken kind)
@@ -556,7 +556,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// </summary>
 		IType UnpackGenericArrayInterface(IType interfaceType)
 		{
-			ParameterizedType pt = interfaceType as ParameterizedType;
+			ParameterizedType? pt = interfaceType as ParameterizedType;
 			if (pt != null)
 			{
 				switch (pt.GetDefinition()?.KnownTypeCode)
@@ -605,8 +605,8 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			{
 				if (!def.Equals(t.GetDefinition()))
 					return false;
-				ParameterizedType ps = s as ParameterizedType;
-				ParameterizedType pt = t as ParameterizedType;
+				ParameterizedType? ps = s as ParameterizedType;
+				ParameterizedType? pt = t as ParameterizedType;
 				if (ps != null && pt != null)
 				{
 					// C# 4.0 spec: §13.1.3.2 Variance Conversion
@@ -700,8 +700,8 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				ITypeDefinition def = fromType.GetDefinition();
 				if (def == null || !def.Equals(toType.GetDefinition()))
 					return false;
-				ParameterizedType ps = fromType as ParameterizedType;
-				ParameterizedType pt = toType as ParameterizedType;
+				ParameterizedType? ps = fromType as ParameterizedType;
+				ParameterizedType? pt = toType as ParameterizedType;
 				if (ps == null || pt == null)
 				{
 					// non-generic delegate - return true for the identity conversion
@@ -940,7 +940,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 		IType FindMostEncompassedType(IEnumerable<IType> candidates)
 		{
-			IType best = null;
+			IType? best = null;
 			foreach (var current in candidates)
 			{
 				if (best == null || IsEncompassedBy(current, best))
@@ -953,7 +953,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 		IType FindMostEncompassingType(IEnumerable<IType> candidates)
 		{
-			IType best = null;
+			IType? best = null;
 			foreach (var current in candidates)
 			{
 				if (best == null || IsEncompassedBy(best, current))
@@ -1179,7 +1179,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		Conversion AnonymousFunctionConversion(ResolveResult resolveResult, IType toType)
 		{
 			// C# 5.0 spec §6.5 Anonymous function conversions
-			LambdaResolveResult f = resolveResult as LambdaResolveResult;
+			LambdaResolveResult? f = resolveResult as LambdaResolveResult;
 			if (f == null)
 				return Conversion.None;
 			if (!f.IsAnonymousMethod)
@@ -1245,7 +1245,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 		static IType UnpackExpressionTreeType(IType type)
 		{
-			ParameterizedType pt = type as ParameterizedType;
+			ParameterizedType? pt = type as ParameterizedType;
 			if (pt != null && pt.TypeParameterCount == 1 && pt.Name == "Expression" && pt.Namespace == "System.Linq.Expressions")
 			{
 				return pt.GetTypeArgument(0);
@@ -1261,7 +1261,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		Conversion MethodGroupConversion(ResolveResult resolveResult, IType toType)
 		{
 			// C# 4.0 spec §6.6 Method group conversions
-			MethodGroupResolveResult rr = resolveResult as MethodGroupResolveResult;
+			MethodGroupResolveResult? rr = resolveResult as MethodGroupResolveResult;
 			if (rr == null)
 				return Conversion.None;
 			IMethod invoke = toType.GetDelegateInvokeMethod();
@@ -1430,7 +1430,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// <returns>0 = neither is better; 1 = t1 is better; 2 = t2 is better</returns>
 		public int BetterConversion(ResolveResult resolveResult, IType t1, IType t2)
 		{
-			LambdaResolveResult lambda = resolveResult as LambdaResolveResult;
+			LambdaResolveResult? lambda = resolveResult as LambdaResolveResult;
 			if (lambda != null)
 			{
 				if (!lambda.IsAnonymousMethod)
@@ -1484,7 +1484,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// </summary>
 		static IType UnpackTask(IType type)
 		{
-			ParameterizedType pt = type as ParameterizedType;
+			ParameterizedType? pt = type as ParameterizedType;
 			if (pt != null && pt.TypeParameterCount == 1 && pt.Name == "Task" && pt.Namespace == "System.Threading.Tasks")
 			{
 				return pt.GetTypeArgument(0);

ICSharpCode.Decompiler/CSharp/Resolver/CSharpInvocationResolveResult.cs

@@ -57,9 +57,9 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			bool isExtensionMethodInvocation = false,
 			bool isExpandedForm = false,
 			bool isDelegateInvocation = false,
-			IReadOnlyList<int> argumentToParameterMap = null,
-			IList<ResolveResult> initializerStatements = null,
-			IType returnTypeOverride = null
+			IReadOnlyList<int>? argumentToParameterMap = null,
+			IList<ResolveResult>? initializerStatements = null,
+			IType? returnTypeOverride = null
 		)
 			: base(targetResult, member, arguments, initializerStatements, returnTypeOverride)
 		{
@@ -88,7 +88,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		public override IList<ResolveResult> GetArgumentsForCall()
 		{
 			ResolveResult[] results = new ResolveResult[Member.Parameters.Count];
-			List<ResolveResult> paramsArguments = IsExpandedForm ? new List<ResolveResult>() : null;
+			List<ResolveResult>? paramsArguments = IsExpandedForm ? new List<ResolveResult>() : null;
 			// map arguments to parameters:
 			for (int i = 0; i < Arguments.Count; i++)
 			{

ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs

@@ -193,7 +193,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			if (this.CurrentTypeDefinition == typeDefinition)
 				return this;
 
-			TypeDefinitionCache newTypeDefinitionCache;
+			TypeDefinitionCache? newTypeDefinitionCache;
 			if (typeDefinition != null)
 				newTypeDefinitionCache = new TypeDefinitionCache(typeDefinition);
 			else
@@ -344,7 +344,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				switch (op)
 				{
 					case UnaryOperatorType.Dereference:
-						PointerType p = expression.Type as PointerType;
+						PointerType? p = expression.Type as PointerType;
 						if (p != null)
 							return UnaryOperatorResolveResult(p.ElementType, op, expression);
 						else
@@ -357,7 +357,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 						ResolveResult getAwaiterInvocation = ResolveInvocation(getAwaiterMethodGroup, Empty<ResolveResult>.Array, argumentNames: null, allowOptionalParameters: false);
 
 						var lookup = CreateMemberLookup();
-						IMethod getResultMethod;
+						IMethod? getResultMethod;
 						IType awaitResultType;
 						var getResultMethodGroup = lookup.Lookup(getAwaiterInvocation, "GetResult", EmptyList<IType>.Instance, true) as MethodGroupResolveResult;
 						if (getResultMethodGroup != null)
@@ -1490,7 +1490,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 						}
 					}
 					// Look in parameters of current method
-					IParameterizedMember parameterizedMember = this.CurrentMember as IParameterizedMember;
+					IParameterizedMember? parameterizedMember = this.CurrentMember as IParameterizedMember;
 					if (parameterizedMember != null)
 					{
 						foreach (IParameter p in parameterizedMember.Parameters)
@@ -1504,7 +1504,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				}
 
 				// look in type parameters of current method
-				IMethod m = this.CurrentMember as IMethod;
+				IMethod? m = this.CurrentMember as IMethod;
 				if (m != null)
 				{
 					foreach (ITypeParameter tp in m.TypeParameters)
@@ -1517,10 +1517,10 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 			bool parameterizeResultType = !(typeArguments.Count != 0 && typeArguments.All(t => t.Kind == TypeKind.UnboundTypeArgument));
 
-			ResolveResult r = null;
+			ResolveResult? r = null;
 			if (currentTypeDefinitionCache != null)
 			{
-				Dictionary<string, ResolveResult> cache = null;
+				Dictionary<string, ResolveResult>? cache = null;
 				bool foundInCache = false;
 				if (k == 0)
 				{
@@ -1597,7 +1597,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 		}
 
-		public bool IsVariableReferenceWithSameType(ResolveResult rr, string identifier, out TypeResolveResult trr)
+		public bool IsVariableReferenceWithSameType(ResolveResult rr, string identifier, out TypeResolveResult? trr)
 		{
 			if (!(rr is MemberResolveResult || rr is LocalResolveResult))
 			{
@@ -1680,7 +1680,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				// finally, look in the imported namespaces:
 				if (!(isInUsingDeclaration && u == currentUsingScope))
 				{
-					IType firstResult = null;
+					IType? firstResult = null;
 					foreach (var importedNamespace in u.Usings)
 					{
 						ITypeDefinition def = importedNamespace.GetTypeDefinition(identifier, typeArguments.Count);
@@ -1794,7 +1794,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			// C# 4.0 spec: §7.6.4
 
 			bool parameterizeResultType = !(typeArguments.Count != 0 && typeArguments.All(t => t.Kind == TypeKind.UnboundTypeArgument));
-			NamespaceResolveResult nrr = target as NamespaceResolveResult;
+			NamespaceResolveResult? nrr = target as NamespaceResolveResult;
 			if (nrr != null)
 			{
 				return ResolveMemberAccessOnNamespace(nrr, identifier, typeArguments, parameterizeResultType);
@@ -1838,7 +1838,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 			else
 			{
-				MethodGroupResolveResult mgrr = result as MethodGroupResolveResult;
+				MethodGroupResolveResult? mgrr = result as MethodGroupResolveResult;
 				if (mgrr != null)
 				{
 					Debug.Assert(mgrr.extensionMethods == null);
@@ -1914,7 +1914,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 			IType collectionType, enumeratorType, elementType;
 			ResolveResult getEnumeratorInvocation;
-			ResolveResult currentRR = null;
+			ResolveResult? currentRR = null;
 			// C# 4.0 spec: §8.8.4 The foreach statement
 			if (expression.Type.Kind == TypeKind.Array || expression.Type.Kind == TypeKind.Dynamic)
 			{
@@ -1958,7 +1958,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					CheckForEnumerableInterface(expression, out collectionType, out enumeratorType, out elementType, out getEnumeratorInvocation);
 				}
 			}
-			IMethod moveNextMethod = null;
+			IMethod? moveNextMethod = null;
 			var moveNextMethodGroup = memberLookup.Lookup(new ResolveResult(enumeratorType), "MoveNext", EmptyList<IType>.Instance, false) as MethodGroupResolveResult;
 			if (moveNextMethodGroup != null)
 			{
@@ -1970,7 +1970,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 			if (currentRR == null)
 				currentRR = memberLookup.Lookup(new ResolveResult(enumeratorType), "Current", EmptyList<IType>.Instance, false);
-			IProperty currentProperty = null;
+			IProperty? currentProperty = null;
 			if (currentRR is MemberResolveResult)
 				currentProperty = ((MemberResolveResult)currentRR).Member as IProperty;
 
@@ -2030,7 +2030,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		///    new List { all extensions from SomeExtensions }
 		/// }
 		/// </remarks>
-		public List<List<IMethod>> GetExtensionMethods(string name = null, IReadOnlyList<IType> typeArguments = null)
+		public List<List<IMethod>> GetExtensionMethods(string? name = null, IReadOnlyList<IType>? typeArguments = null)
 		{
 			return GetExtensionMethods(null, name, typeArguments);
 		}
@@ -2059,7 +2059,7 @@ 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>>();
@@ -2127,7 +2127,7 @@ 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)
@@ -2248,7 +2248,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 
 			bool isDynamic = arguments.Any(a => a.Type.Kind == TypeKind.Dynamic);
-			MethodGroupResolveResult mgrr = target as MethodGroupResolveResult;
+			MethodGroupResolveResult? mgrr = target as MethodGroupResolveResult;
 			if (mgrr != null)
 			{
 				if (isDynamic)
@@ -2292,12 +2292,12 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 						mgrr.TargetType, mgrr.MethodName, mgrr.TypeArguments, CreateParameters(arguments, argumentNames));
 				}
 			}
-			UnknownMemberResolveResult umrr = target as UnknownMemberResolveResult;
+			UnknownMemberResolveResult? umrr = target as UnknownMemberResolveResult;
 			if (umrr != null)
 			{
 				return new UnknownMethodResolveResult(umrr.TargetType, umrr.MemberName, umrr.TypeArguments, CreateParameters(arguments, argumentNames));
 			}
-			UnknownIdentifierResolveResult uirr = target as UnknownIdentifierResolveResult;
+			UnknownIdentifierResolveResult? uirr = target as UnknownIdentifierResolveResult;
 			if (uirr != null && CurrentTypeDefinition != null)
 			{
 				return new UnknownMethodResolveResult(CurrentTypeDefinition, uirr.Identifier, EmptyList<IType>.Instance, CreateParameters(arguments, argumentNames));
@@ -2330,7 +2330,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// The argument names. Pass the null string for positional arguments.
 		/// </param>
 		/// <returns>InvocationResolveResult or UnknownMethodResolveResult</returns>
-		public ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[] argumentNames = null)
+		public ResolveResult ResolveInvocation(ResolveResult target, ResolveResult[] arguments, string[]? argumentNames = null)
 		{
 			return ResolveInvocation(target, arguments, argumentNames, allowOptionalParameters: true);
 		}
@@ -2370,7 +2370,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				}
 
 				// create the parameter:
-				ByReferenceResolveResult brrr = arguments[i] as ByReferenceResolveResult;
+				ByReferenceResolveResult? brrr = arguments[i] as ByReferenceResolveResult;
 				if (brrr != null)
 				{
 					list.Add(new DefaultParameter(arguments[i].Type, argumentNames[i], referenceKind: brrr.ReferenceKind));
@@ -2394,19 +2394,19 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 		static string GuessParameterName(ResolveResult rr)
 		{
-			MemberResolveResult mrr = rr as MemberResolveResult;
+			MemberResolveResult? mrr = rr as MemberResolveResult;
 			if (mrr != null)
 				return mrr.Member.Name;
 
-			UnknownMemberResolveResult umrr = rr as UnknownMemberResolveResult;
+			UnknownMemberResolveResult? umrr = rr as UnknownMemberResolveResult;
 			if (umrr != null)
 				return umrr.MemberName;
 
-			MethodGroupResolveResult mgrr = rr as MethodGroupResolveResult;
+			MethodGroupResolveResult? mgrr = rr as MethodGroupResolveResult;
 			if (mgrr != null)
 				return mgrr.MethodName;
 
-			LocalResolveResult vrr = rr as LocalResolveResult;
+			LocalResolveResult? vrr = rr as LocalResolveResult;
 			if (vrr != null)
 				return MakeParameterName(vrr.Variable.Name);
 
@@ -2429,7 +2429,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return char.ToLower(variableName[0]) + variableName.Substring(1);
 		}
 
-		OverloadResolution CreateOverloadResolution(ResolveResult[] arguments, string[] argumentNames = null, IType[] typeArguments = null)
+		OverloadResolution CreateOverloadResolution(ResolveResult[] arguments, string[]? argumentNames = null, IType[]? typeArguments = null)
 		{
 			var or = new OverloadResolution(compilation, arguments, argumentNames, typeArguments, conversions);
 			or.CheckForOverflow = checkForOverflow;
@@ -2450,7 +2450,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// The argument names. Pass the null string for positional arguments.
 		/// </param>
 		/// <returns>ArrayAccessResolveResult, InvocationResolveResult, or ErrorResolveResult</returns>
-		public ResolveResult ResolveIndexer(ResolveResult target, ResolveResult[] arguments, string[] argumentNames = null)
+		public ResolveResult ResolveIndexer(ResolveResult target, ResolveResult[] arguments, string[]? argumentNames = null)
 		{
 			switch (target.Type.Kind)
 			{
@@ -2533,7 +2533,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// <see cref="InvocationResolveResult.InitializerStatements"/>
 		/// </param>
 		/// <returns>InvocationResolveResult or ErrorResolveResult</returns>
-		public ResolveResult ResolveObjectCreation(IType type, ResolveResult[] arguments, string[] argumentNames = null, bool allowProtectedAccess = false, IList<ResolveResult> initializerStatements = null)
+		public ResolveResult ResolveObjectCreation(IType type, ResolveResult[] arguments, string[]? argumentNames = null, bool allowProtectedAccess = false, IList<ResolveResult>? initializerStatements = null)
 		{
 			if (type.Kind == TypeKind.Delegate && arguments.Length == 1)
 			{
@@ -2875,7 +2875,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// The initializer elements. May be null if no array initializer was specified.
 		/// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
 		/// </param>
-		public ArrayCreateResolveResult ResolveArrayCreation(IType elementType, int[] sizeArguments, ResolveResult[] initializerElements = null)
+		public ArrayCreateResolveResult ResolveArrayCreation(IType elementType, int[] sizeArguments, ResolveResult[]? initializerElements = null)
 		{
 			ResolveResult[] sizeArgResults = new ResolveResult[sizeArguments.Length];
 			for (int i = 0; i < sizeArguments.Length; i++)
@@ -2904,7 +2904,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// The initializer elements. May be null if no array initializer was specified.
 		/// The resolver may mutate this array to wrap elements in <see cref="ConversionResolveResult"/>s!
 		/// </param>
-		public ArrayCreateResolveResult ResolveArrayCreation(IType elementType, ResolveResult[] sizeArguments, ResolveResult[] initializerElements = null)
+		public ArrayCreateResolveResult ResolveArrayCreation(IType elementType, ResolveResult[] sizeArguments, ResolveResult[]? initializerElements = null)
 		{
 			int dimensions = sizeArguments.Length;
 			if (dimensions == 0)
@@ -2944,7 +2944,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				return new OperatorResolveResult(lhs.Type, linqOp, lhs, this.Convert(rhs, lhs.Type));
 			}
 			ResolveResult bopResult = ResolveBinaryOperator(bop.Value, lhs, rhs);
-			OperatorResolveResult opResult = bopResult as OperatorResolveResult;
+			OperatorResolveResult? opResult = bopResult as OperatorResolveResult;
 			if (opResult == null || opResult.Operands.Count != 2)
 				return bopResult;
 			return new OperatorResolveResult(lhs.Type, linqOp, opResult.UserDefinedOperatorMethod, opResult.IsLiftedOperator,

ICSharpCode.Decompiler/CSharp/Resolver/DynamicInvocationResolveResult.cs

@@ -72,7 +72,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// </summary>
 		public readonly IList<ResolveResult> InitializerStatements;
 
-		public DynamicInvocationResolveResult(ResolveResult target, DynamicInvocationType invocationType, IList<ResolveResult> arguments, IList<ResolveResult> initializerStatements = null) : base(SpecialType.Dynamic)
+		public DynamicInvocationResolveResult(ResolveResult target, DynamicInvocationType invocationType, IList<ResolveResult> arguments, IList<ResolveResult>? initializerStatements = null) : base(SpecialType.Dynamic)
 		{
 			this.Target = target;
 			this.InvocationType = invocationType;

ICSharpCode.Decompiler/CSharp/Resolver/MemberLookup.cs

@@ -199,11 +199,11 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					if (!lookupGroupDict.TryGetValue(entityGroup.Key, out lookupGroups))
 						lookupGroupDict.Add(entityGroup.Key, lookupGroups = new List<LookupGroup>());
 
-					List<IType> newNestedTypes = null;
-					List<IParameterizedMember> newMethods = null;
-					IMember newNonMethod = null;
+					List<IType>? newNestedTypes = null;
+					List<IParameterizedMember>? newMethods = null;
+					IMember? newNonMethod = null;
 
-					IEnumerable<IType> typeBaseTypes = null;
+					IEnumerable<IType>? typeBaseTypes = null;
 
 					if (!targetIsTypeParameter)
 					{
@@ -310,8 +310,8 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			{
 				foreach (IType type in declaringType.GetNonInterfaceBaseTypes())
 				{
-					List<IType> newNestedTypes = null;
-					IEnumerable<IType> typeBaseTypes = null;
+					List<IType>? newNestedTypes = null;
+					IEnumerable<IType>? typeBaseTypes = null;
 
 					IEnumerable<IType> nestedTypes;
 					if (parameterizeResultType)
@@ -389,11 +389,11 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			foreach (IType type in targetResolveResult.Type.GetNonInterfaceBaseTypes())
 			{
 
-				List<IType> newNestedTypes = null;
-				List<IParameterizedMember> newMethods = null;
-				IMember newNonMethod = null;
+				List<IType>? newNestedTypes = null;
+				List<IParameterizedMember>? newMethods = null;
+				IMember? newNonMethod = null;
 
-				IEnumerable<IType> typeBaseTypes = null;
+				IEnumerable<IType>? typeBaseTypes = null;
 
 				if (!isInvocation && !targetIsTypeParameter)
 				{
@@ -452,10 +452,10 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			List<LookupGroup> lookupGroups = new List<LookupGroup>();
 			foreach (IType type in targetType.GetNonInterfaceBaseTypes())
 			{
-				List<IParameterizedMember> newMethods = null;
-				IMember newNonMethod = null;
+				List<IParameterizedMember>? newMethods = null;
+				IMember? newNonMethod = null;
 
-				IEnumerable<IType> typeBaseTypes = null;
+				IEnumerable<IType>? typeBaseTypes = null;
 
 				var members = type.GetProperties(filter, GetMemberOptions.IgnoreInheritedMembers);
 				AddMembers(type, members, allowProtectedAccess, lookupGroups, true, ref typeBaseTypes, ref newMethods, ref newNonMethod);
@@ -551,7 +551,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				if (!IsAccessible(member, allowProtectedAccess))
 					continue;
 
-				IParameterizedMember method;
+				IParameterizedMember? method;
 				if (treatAllParameterizedMembersAsMethods)
 					method = member as IParameterizedMember;
 				else
@@ -753,7 +753,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			{
 				if (isInEnumMemberInitializer)
 				{
-					IField field = resultGroup.NonMethod as IField;
+					IField? field = resultGroup.NonMethod as IField;
 					if (field != null && field.DeclaringTypeDefinition != null && field.DeclaringTypeDefinition.Kind == TypeKind.Enum)
 					{
 						return new MemberResolveResult(

ICSharpCode.Decompiler/CSharp/Resolver/MethodGroupResolveResult.cs

@@ -229,12 +229,12 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			return string.Format("[{0} with {1} method(s)]", GetType().Name, this.Methods.Count());
 		}
 
-		public OverloadResolution PerformOverloadResolution(ICompilation compilation, ResolveResult[] arguments, string[] argumentNames = null,
+		public OverloadResolution PerformOverloadResolution(ICompilation compilation, ResolveResult[] arguments, string[]? argumentNames = null,
 															bool allowExtensionMethods = true,
 															bool allowExpandingParams = true,
 															bool allowOptionalParameters = true,
 															bool allowImplicitIn = true,
-															bool checkForOverflow = false, CSharpConversions conversions = null)
+															bool checkForOverflow = false, CSharpConversions? conversions = null)
 		{
 			Log.WriteLine("Performing overload resolution for " + this);
 			Log.WriteCollection("  Arguments: ", arguments);
@@ -260,7 +260,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					ResolveResult[] extArguments = new ResolveResult[arguments.Length + 1];
 					extArguments[0] = new ResolveResult(this.TargetType);
 					arguments.CopyTo(extArguments, 1);
-					string[] extArgumentNames = null;
+					string[]? extArgumentNames = null;
 					if (argumentNames != null)
 					{
 						extArgumentNames = new string[argumentNames.Length + 1];

ICSharpCode.Decompiler/CSharp/Resolver/OverloadResolution.cs

@@ -78,7 +78,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 
 			public bool IsGenericMethod {
 				get {
-					IMethod method = Member as IMethod;
+					IMethod? method = Member as IMethod;
 					return method != null && method.TypeParameters.Count > 0;
 				}
 			}
@@ -108,7 +108,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				// (without any type parameter substitution, not even class type parameters)
 				// We'll re-substitute them as part of RunTypeInference().
 				this.Parameters = memberDefinition.Parameters;
-				IMethod methodDefinition = memberDefinition as IMethod;
+				IMethod? methodDefinition = memberDefinition as IMethod;
 				if (methodDefinition != null && methodDefinition.TypeParameters.Count > 0)
 				{
 					this.TypeParameters = methodDefinition.TypeParameters;
@@ -136,7 +136,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		OverloadResolutionErrors bestCandidateValidationResult;
 
 		#region Constructor
-		public OverloadResolution(ICompilation compilation, ResolveResult[] arguments, string[] argumentNames = null, IType[] typeArguments = null, CSharpConversions conversions = null)
+		public OverloadResolution(ICompilation compilation, ResolveResult[] arguments, string[]? argumentNames = null, IType[]? typeArguments = null, CSharpConversions? conversions = null)
 		{
 			if (compilation == null)
 				throw new ArgumentNullException(nameof(compilation));
@@ -286,7 +286,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				}
 				if (candidate.IsExpandedForm && i == candidate.Parameters.Count - 1)
 				{
-					ArrayType arrayType = type as ArrayType;
+					ArrayType? arrayType = type as ArrayType;
 					if (arrayType != null && arrayType.Dimensions == 1)
 						type = arrayType.ElementType;
 					else
@@ -311,7 +311,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			if (methodLists == null)
 				throw new ArgumentNullException(nameof(methodLists));
 			// Base types come first, so go through the list backwards (derived types first)
-			bool[] isHiddenByDerivedType;
+			bool[]? isHiddenByDerivedType;
 			if (methodLists.Count > 1)
 				isHiddenByDerivedType = new bool[methodLists.Count];
 			else
@@ -436,8 +436,8 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				ResolveParameterTypes(candidate, true);
 				return;
 			}
-			ParameterizedType parameterizedDeclaringType = candidate.Member.DeclaringType as ParameterizedType;
-			IReadOnlyList<IType> classTypeArguments;
+			ParameterizedType? parameterizedDeclaringType = candidate.Member.DeclaringType as ParameterizedType;
+			IReadOnlyList<IType>? classTypeArguments;
 			if (parameterizedDeclaringType != null)
 			{
 				classTypeArguments = parameterizedDeclaringType.TypeArguments;
@@ -504,7 +504,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				if (newType != type && ConstraintsValid)
 				{
 					// something was changed, so we need to validate the constraints
-					ParameterizedType newParameterizedType = newType as ParameterizedType;
+					ParameterizedType? newParameterizedType = newType as ParameterizedType;
 					if (newParameterizedType != null)
 					{
 						// C# 4.0 spec: §4.4.4 Satisfying constraints
@@ -552,7 +552,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// The substitution is used to check constraints that depend on other type parameters (or recursively on the same type parameter).
 		/// May be null if no substitution should be used.</param>
 		/// <returns>True if the constraints are satisfied; false otherwise.</returns>
-		public static bool ValidateConstraints(ITypeParameter typeParameter, IType typeArgument, TypeVisitor substitution = null)
+		public static bool ValidateConstraints(ITypeParameter typeParameter, IType typeArgument, TypeVisitor? substitution = null)
 		{
 			if (typeParameter == null)
 				throw new ArgumentNullException(nameof(typeParameter));
@@ -791,8 +791,8 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					return r;
 
 				// prefer non-lifted operators
-				ILiftedOperator lift1 = c1.Member as ILiftedOperator;
-				ILiftedOperator lift2 = c2.Member as ILiftedOperator;
+				ILiftedOperator? lift1 = c1.Member as ILiftedOperator;
+				ILiftedOperator? lift2 = c2.Member as ILiftedOperator;
 				if (lift1 == null && lift2 != null)
 					return 1;
 				if (lift1 != null && lift2 == null)
@@ -843,16 +843,16 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			if ((t2 is ITypeParameter) && !(t1 is ITypeParameter))
 				return 1;
 
-			ParameterizedType p1 = t1 as ParameterizedType;
-			ParameterizedType p2 = t2 as ParameterizedType;
+			ParameterizedType? p1 = t1 as ParameterizedType;
+			ParameterizedType? p2 = t2 as ParameterizedType;
 			if (p1 != null && p2 != null && p1.TypeParameterCount == p2.TypeParameterCount)
 			{
 				int r = MoreSpecificFormalParameters(p1.TypeArguments, p2.TypeArguments);
 				if (r > 0)
 					return r;
 			}
-			TypeWithElementType tew1 = t1 as TypeWithElementType;
-			TypeWithElementType tew2 = t2 as TypeWithElementType;
+			TypeWithElementType? tew1 = t1 as TypeWithElementType;
+			TypeWithElementType? tew2 = t2 as TypeWithElementType;
 			if (tew1 != null && tew2 != null)
 			{
 				return MoreSpecificFormalParameter(tew1.ElementType, tew2.ElementType);
@@ -1041,7 +1041,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		{
 			if (bestCandidate == null)
 				return null;
-			IMethod method = bestCandidate.Member as IMethod;
+			IMethod? method = bestCandidate.Member as IMethod;
 			if (method != null && method.TypeParameters.Count > 0)
 			{
 				return ((IMethod)method.MemberDefinition).Specialize(GetSubstitution(bestCandidate));
@@ -1072,7 +1072,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// <param name="returnTypeOverride">
 		/// If not null, use this instead of the ReturnType of the member as the type of the created resolve result.
 		/// </param>
-		public CSharpInvocationResolveResult CreateResolveResult(ResolveResult targetResolveResult, IList<ResolveResult> initializerStatements = null, IType returnTypeOverride = null)
+		public CSharpInvocationResolveResult CreateResolveResult(ResolveResult targetResolveResult, IList<ResolveResult>? initializerStatements = null, IType? returnTypeOverride = null)
 		{
 			IParameterizedMember member = GetBestCandidateWithSubstitutedTypeArguments();
 			if (member == null)

ICSharpCode.Decompiler/CSharp/Resolver/TypeInference.cs

@@ -113,7 +113,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		/// when inferring a method group or lambda.
 		/// </param>
 		/// <returns>The inferred type arguments.</returns>
-		public IType[] InferTypeArguments(IReadOnlyList<ITypeParameter> typeParameters, IReadOnlyList<ResolveResult> arguments, IReadOnlyList<IType> parameterTypes, out bool success, IReadOnlyList<IType> classTypeArguments = null)
+		public IType[] InferTypeArguments(IReadOnlyList<ITypeParameter> typeParameters, IReadOnlyList<ResolveResult> arguments, IReadOnlyList<IType> parameterTypes, out bool success, IReadOnlyList<IType>? classTypeArguments = null)
 		{
 			if (typeParameters == null)
 				throw new ArgumentNullException(nameof(typeParameters));
@@ -283,7 +283,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				ResolveResult Ei = arguments[i];
 				IType Ti = parameterTypes[i];
 
-				LambdaResolveResult lrr = Ei as LambdaResolveResult;
+				LambdaResolveResult? lrr = Ei as LambdaResolveResult;
 				if (lrr != null)
 				{
 					MakeExplicitParameterTypeInference(lrr, Ti);
@@ -397,7 +397,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		IType[] InputTypes(ResolveResult e, IType t)
 		{
 			// C# 4.0 spec: §7.5.2.3 Input types
-			LambdaResolveResult lrr = e as LambdaResolveResult;
+			LambdaResolveResult? lrr = e as LambdaResolveResult;
 			if (lrr != null && lrr.IsImplicitlyTyped || e is MethodGroupResolveResult)
 			{
 				IMethod m = GetDelegateOrExpressionTreeSignature(t);
@@ -417,7 +417,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 		IType[] OutputTypes(ResolveResult e, IType t)
 		{
 			// C# 4.0 spec: §7.5.2.4 Output types
-			LambdaResolveResult lrr = e as LambdaResolveResult;
+			LambdaResolveResult? lrr = e as LambdaResolveResult;
 			if (lrr != null || e is MethodGroupResolveResult)
 			{
 				IMethod m = GetDelegateOrExpressionTreeSignature(t);
@@ -524,7 +524,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			Log.WriteLine(" MakeOutputTypeInference from " + e + " to " + t);
 			// If E is an anonymous function with inferred return type  U (§7.5.2.12) and T is a delegate type or expression
 			// tree type with return type Tb, then a lower-bound inference (§7.5.2.9) is made from U to Tb.
-			LambdaResolveResult lrr = e as LambdaResolveResult;
+			LambdaResolveResult? lrr = e as LambdaResolveResult;
 			if (lrr != null)
 			{
 				IMethod m = GetDelegateOrExpressionTreeSignature(t);
@@ -556,7 +556,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			// with parameter types T1…Tk and return type Tb, and overload resolution
 			// of E with the types T1…Tk yields a single method with return type U, then a lower­-bound
 			// inference is made from U to Tb.
-			MethodGroupResolveResult mgrr = e as MethodGroupResolveResult;
+			MethodGroupResolveResult? mgrr = e as MethodGroupResolveResult;
 			if (mgrr != null)
 			{
 				IMethod m = GetDelegateOrExpressionTreeSignature(t);
@@ -651,24 +651,24 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				return;
 			}
 			// Handle by reference types:
-			ByReferenceType brU = U as ByReferenceType;
-			ByReferenceType brV = V as ByReferenceType;
+			ByReferenceType? brU = U as ByReferenceType;
+			ByReferenceType? brV = V as ByReferenceType;
 			if (brU != null && brV != null)
 			{
 				MakeExactInference(brU.ElementType, brV.ElementType);
 				return;
 			}
 			// Handle array types:
-			ArrayType arrU = U as ArrayType;
-			ArrayType arrV = V as ArrayType;
+			ArrayType? arrU = U as ArrayType;
+			ArrayType? arrV = V as ArrayType;
 			if (arrU != null && arrV != null && arrU.Dimensions == arrV.Dimensions)
 			{
 				MakeExactInference(arrU.ElementType, arrV.ElementType);
 				return;
 			}
 			// Handle parameterized type:
-			ParameterizedType pU = U.TupleUnderlyingTypeOrSelf() as ParameterizedType;
-			ParameterizedType pV = V.TupleUnderlyingTypeOrSelf() as ParameterizedType;
+			ParameterizedType? pU = U.TupleUnderlyingTypeOrSelf() as ParameterizedType;
+			ParameterizedType? pV = V.TupleUnderlyingTypeOrSelf() as ParameterizedType;
 			if (pU != null && pV != null
 				&& object.Equals(pU.GenericType, pV.GenericType)
 				&& pU.TypeParameterCount == pV.TypeParameterCount)
@@ -743,17 +743,17 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				return;
 			}
 			// Handle by reference types:
-			ByReferenceType brU = U as ByReferenceType;
-			ByReferenceType brV = V as ByReferenceType;
+			ByReferenceType? brU = U as ByReferenceType;
+			ByReferenceType? brV = V as ByReferenceType;
 			if (brU != null && brV != null)
 			{
 				MakeExactInference(brU.ElementType, brV.ElementType);
 				return;
 			}
 			// Handle array types:
-			ArrayType arrU = U as ArrayType;
-			ArrayType arrV = V as ArrayType;
-			ParameterizedType pV = V.TupleUnderlyingTypeOrSelf() as ParameterizedType;
+			ArrayType? arrU = U as ArrayType;
+			ArrayType? arrV = V as ArrayType;
+			ParameterizedType? pV = V.TupleUnderlyingTypeOrSelf() as ParameterizedType;
 			if (arrU != null && arrV != null && arrU.Dimensions == arrV.Dimensions)
 			{
 				MakeLowerBoundInference(arrU.ElementType, arrV.ElementType);
@@ -767,10 +767,10 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			// Handle parameterized types:
 			if (pV != null)
 			{
-				ParameterizedType uniqueBaseType = null;
+				ParameterizedType? uniqueBaseType = null;
 				foreach (IType baseU in U.GetAllBaseTypes())
 				{
-					ParameterizedType pU = baseU.TupleUnderlyingTypeOrSelf() as ParameterizedType;
+					ParameterizedType? pU = baseU.TupleUnderlyingTypeOrSelf() as ParameterizedType;
 					if (pU != null && object.Equals(pU.GenericType, pV.GenericType) && pU.TypeParameterCount == pV.TypeParameterCount)
 					{
 						if (uniqueBaseType == null)
@@ -872,9 +872,9 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			}
 
 			// Handle array types:
-			ArrayType arrU = U as ArrayType;
-			ArrayType arrV = V as ArrayType;
-			ParameterizedType pU = U.TupleUnderlyingTypeOrSelf() as ParameterizedType;
+			ArrayType? arrU = U as ArrayType;
+			ArrayType? arrV = V as ArrayType;
+			ParameterizedType? pU = U.TupleUnderlyingTypeOrSelf() as ParameterizedType;
 			if (arrV != null && arrU != null && arrU.Dimensions == arrV.Dimensions)
 			{
 				MakeUpperBoundInference(arrU.ElementType, arrV.ElementType);
@@ -888,10 +888,10 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			// Handle parameterized types:
 			if (pU != null)
 			{
-				ParameterizedType uniqueBaseType = null;
+				ParameterizedType? uniqueBaseType = null;
 				foreach (IType baseV in V.GetAllBaseTypes())
 				{
-					ParameterizedType pV = baseV.TupleUnderlyingTypeOrSelf() as ParameterizedType;
+					ParameterizedType? pV = baseV.TupleUnderlyingTypeOrSelf() as ParameterizedType;
 					if (pV != null && object.Equals(pU.GenericType, pV.GenericType) && pU.TypeParameterCount == pV.TypeParameterCount)
 					{
 						if (uniqueBaseType == null)

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -151,7 +151,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return new IfElseStatement(condition, trueStatement, falseStatement).WithILInstruction(inst);
 		}
 
-		internal IEnumerable<ConstantResolveResult> CreateTypedCaseLabel(long i, IType type, List<(string Key, int Value)> map = null)
+		internal IEnumerable<ConstantResolveResult> CreateTypedCaseLabel(long i, IType type, List<(string Key, int Value)>? map = null)
 		{
 			object value;
 			// unpack nullable type, if necessary:
@@ -243,7 +243,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			foreach (var section in inst.Sections)
 			{
 				// This is used in the block-label mapping.
-				ConstantResolveResult firstValueResolveResult;
+				ConstantResolveResult? firstValueResolveResult;
 				var astSection = new Syntax.SwitchSection();
 				// Create case labels:
 				if (section == defaultSection)
@@ -346,7 +346,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (!bodyInst.HasFlag(InstructionFlags.EndPointUnreachable))
 			{
 				// we need to insert 'break;'
-				BlockStatement block = body as BlockStatement;
+				BlockStatement? block = body as BlockStatement;
 				if (block != null)
 				{
 					block.Add(new BreakStatement());
@@ -731,7 +731,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					break;
 			}
 
-			VariableDesignation designation = null;
+			VariableDesignation? designation = null;
 
 			// Handle the required foreach-variable transformation:
 			switch (transformation)
@@ -875,7 +875,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			return NormalizeTypeVisitor.TypeErasure.EquivalentTypes(a, b);
 		}
 
-		private bool IsDynamicCastToIEnumerable(Expression expr, out Expression dynamicExpr)
+		private bool IsDynamicCastToIEnumerable(Expression expr, out Expression? dynamicExpr)
 		{
 			if (!(expr is CastExpression cast))
 			{
@@ -898,7 +898,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// Otherwise returns the unmodified container.
 		/// </summary>
 		/// <param name="optionalLeaveInst">If the leave is a return/break and has no side-effects, we can move the return out of the using-block and put it after the loop, otherwise returns null.</param>
-		BlockContainer UnwrapNestedContainerIfPossible(BlockContainer container, out Leave optionalLeaveInst)
+		BlockContainer UnwrapNestedContainerIfPossible(BlockContainer container, out Leave? optionalLeaveInst)
 		{
 			optionalLeaveInst = null;
 			// Check block structure:
@@ -978,7 +978,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// <param name="singleGetter">Returns the call instruction invoking Current's getter.</param>
 		/// <param name="foreachVariable">Returns the the foreach variable, if a suitable was found. This variable is only assigned once and its assignment is the first statement in <paramref name="loopBody"/>.</param>
 		/// <returns><see cref="RequiredGetCurrentTransformation"/> for details.</returns>
-		RequiredGetCurrentTransformation DetectGetCurrentTransformation(BlockContainer usingContainer, Block loopBody, BlockContainer loopContainer, ILVariable enumerator, ILInstruction moveNextUsage, out CallInstruction singleGetter, out ILVariable foreachVariable)
+		RequiredGetCurrentTransformation DetectGetCurrentTransformation(BlockContainer usingContainer, Block loopBody, BlockContainer loopContainer, ILVariable enumerator, ILInstruction moveNextUsage, out CallInstruction? singleGetter, out ILVariable? foreachVariable)
 		{
 			singleGetter = null;
 			foreachVariable = null;
@@ -1425,7 +1425,7 @@ namespace ICSharpCode.Decompiler.CSharp
 
 					method.Body = nestedBuilder.ConvertAsBlock(function.Body);
 
-					Comment prev = null;
+					Comment? prev = null;
 					foreach (string warning in function.Warnings)
 					{
 						method.Body.InsertChildAfter(prev, prev = new Comment(warning), Roles.Comment);

ICSharpCode.Decompiler/CSharp/Syntax/AstNodeCollection.cs

@@ -149,7 +149,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// Returns the first element for which the predicate returns true,
 		/// or the null node (AstNode with IsNull=true) if no such object is found.
 		/// </summary>
-		public T FirstOrNullObject(Func<T, bool> predicate = null)
+		public T FirstOrNullObject(Func<T, bool>? predicate = null)
 		{
 			foreach (T item in this)
 				if (predicate == null || predicate(item))
@@ -161,7 +161,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// Returns the last element for which the predicate returns true,
 		/// or the null node (AstNode with IsNull=true) if no such object is found.
 		/// </summary>
-		public T LastOrNullObject(Func<T, bool> predicate = null)
+		public T LastOrNullObject(Func<T, bool>? predicate = null)
 		{
 			T result = role.NullObject;
 			foreach (T item in this)
@@ -202,7 +202,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public override bool Equals(object obj)
 		{
-			AstNodeCollection<T> other = obj as AstNodeCollection<T>;
+			AstNodeCollection<T>? other = obj as AstNodeCollection<T>;
 			if (other == null)
 				return false;
 			return this.node == other.node && this.role == other.role;

ICSharpCode.Decompiler/CSharp/Syntax/AstType.cs

@@ -133,7 +133,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// </summary>
 		public bool IsVar()
 		{
-			SimpleType st = this as SimpleType;
+			SimpleType? st = this as SimpleType;
 			return st != null && st.Identifier == "var" && st.TypeArguments.Count == 0;
 		}
 
@@ -148,7 +148,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// For resolving simple names, the current namespace and usings from the CurrentUsingScope
 		/// (on CSharpTypeResolveContext only) is used.
 		/// </remarks>
-		public ITypeReference ToTypeReference(InterningProvider interningProvider = null)
+		public ITypeReference ToTypeReference(InterningProvider? interningProvider = null)
 		{
 			return ToTypeReference(GetNameLookupMode(), interningProvider);
 		}
@@ -163,7 +163,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// For resolving simple names, the current namespace and usings from the CurrentUsingScope
 		/// (on CSharpTypeResolveContext only) is used.
 		/// </remarks>
-		public abstract ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null);
+		public abstract ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null);
 
 		/// <summary>
 		/// Gets the name lookup mode from the context (looking at the ancestors of this <see cref="AstType"/>).

ICSharpCode.Decompiler/CSharp/Syntax/CSharpModifierToken.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			CSharpModifierToken o = other as CSharpModifierToken;
+			CSharpModifierToken? o = other as CSharpModifierToken;
 			return o != null && this.modifier == o.modifier;
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/CSharpTokenNode.cs

@@ -134,7 +134,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			CSharpTokenNode o = other as CSharpTokenNode;
+			CSharpTokenNode? o = other as CSharpTokenNode;
 			return o != null && !o.IsNull && !(o is CSharpModifierToken);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/ComposedType.cs

@@ -146,7 +146,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ComposedType o = other as ComposedType;
+			ComposedType? o = other as ComposedType;
 			return o != null
 				&& this.HasNullableSpecifier == o.HasNullableSpecifier
 				&& this.PointerRank == o.PointerRank
@@ -201,7 +201,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return this;
 		}
 
-		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null)
+		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null)
 		{
 			if (interningProvider == null)
 				interningProvider = InterningProvider.Dummy;
@@ -289,7 +289,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ArraySpecifier o = other as ArraySpecifier;
+			ArraySpecifier? o = other as ArraySpecifier;
 			return o != null && this.Dimensions == o.Dimensions;
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/DocumentationReference.cs

@@ -111,7 +111,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			DocumentationReference o = other as DocumentationReference;
+			DocumentationReference? o = other as DocumentationReference;
 			if (!(o != null && this.SymbolKind == o.SymbolKind && this.HasParameterList == o.HasParameterList))
 				return false;
 			if (this.SymbolKind == SymbolKind.Operator)

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/AnonymousMethodExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public AnonymousMethodExpression(BlockStatement body, IEnumerable<ParameterDeclaration> parameters = null)
+		public AnonymousMethodExpression(BlockStatement body, IEnumerable<ParameterDeclaration>? parameters = null)
 		{
 			if (parameters != null)
 			{
@@ -111,7 +111,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			AnonymousMethodExpression o = other as AnonymousMethodExpression;
+			AnonymousMethodExpression? o = other as AnonymousMethodExpression;
 			return o != null && this.IsAsync == o.IsAsync && this.HasParameterList == o.HasParameterList
 				&& this.Parameters.DoMatch(o.Parameters, match) && this.Body.DoMatch(o.Body, match);
 		}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ArrayCreateExpression.cs

@@ -71,7 +71,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ArrayCreateExpression o = other as ArrayCreateExpression;
+			ArrayCreateExpression? o = other as ArrayCreateExpression;
 			return o != null && this.Type.DoMatch(o.Type, match)
 				&& this.Arguments.DoMatch(o.Arguments, match)
 				&& this.AdditionalArraySpecifiers.DoMatch(o.AdditionalArraySpecifiers, match)

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ArrayInitializerExpression.cs

@@ -121,7 +121,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ArrayInitializerExpression o = other as ArrayInitializerExpression;
+			ArrayInitializerExpression? o = other as ArrayInitializerExpression;
 			return o != null && this.Elements.DoMatch(o.Elements, match);
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/AsExpression.cs

@@ -75,7 +75,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			AsExpression o = other as AsExpression;
+			AsExpression? o = other as AsExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match) && this.Type.DoMatch(o.Type, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/AssignmentExpression.cs

@@ -105,7 +105,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			AssignmentExpression o = other as AssignmentExpression;
+			AssignmentExpression? o = other as AssignmentExpression;
 			return o != null && (this.Operator == AssignmentOperatorType.Any || this.Operator == o.Operator)
 				&& this.Left.DoMatch(o.Left, match) && this.Right.DoMatch(o.Right, match);
 		}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/BaseReferenceExpression.cs

@@ -65,7 +65,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			BaseReferenceExpression o = other as BaseReferenceExpression;
+			BaseReferenceExpression? o = other as BaseReferenceExpression;
 			return o != null;
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/BinaryOperatorExpression.cs

@@ -107,7 +107,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			BinaryOperatorExpression o = other as BinaryOperatorExpression;
+			BinaryOperatorExpression? o = other as BinaryOperatorExpression;
 			return o != null && (this.Operator == BinaryOperatorType.Any || this.Operator == o.Operator)
 				&& this.Left.DoMatch(o.Left, match) && this.Right.DoMatch(o.Right, match);
 		}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/CastExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			CastExpression o = other as CastExpression;
+			CastExpression? o = other as CastExpression;
 			return o != null && this.Type.DoMatch(o.Type, match) && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/CheckedExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			CheckedExpression o = other as CheckedExpression;
+			CheckedExpression? o = other as CheckedExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ConditionalExpression.cs

@@ -89,7 +89,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ConditionalExpression o = other as ConditionalExpression;
+			ConditionalExpression? o = other as ConditionalExpression;
 			return o != null && this.Condition.DoMatch(o.Condition, match) && this.TrueExpression.DoMatch(o.TrueExpression, match) && this.FalseExpression.DoMatch(o.FalseExpression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/DefaultValueExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			DefaultValueExpression o = other as DefaultValueExpression;
+			DefaultValueExpression? o = other as DefaultValueExpression;
 			return o != null && this.Type.DoMatch(o.Type, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/DirectionExpression.cs

@@ -95,7 +95,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			DirectionExpression o = other as DirectionExpression;
+			DirectionExpression? o = other as DirectionExpression;
 			return o != null && this.FieldDirection == o.FieldDirection && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/IdentifierExpression.cs

@@ -81,7 +81,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			IdentifierExpression o = other as IdentifierExpression;
+			IdentifierExpression? o = other as IdentifierExpression;
 			return o != null && MatchString(this.Identifier, o.Identifier) && this.TypeArguments.DoMatch(o.TypeArguments, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/IndexerExpression.cs

@@ -54,7 +54,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public IndexerExpression(Expression target, IEnumerable<Expression> arguments)
+		public IndexerExpression(Expression target, IEnumerable<Expression>? arguments)
 		{
 			AddChild(target, Roles.TargetExpression);
 			if (arguments != null)
@@ -66,7 +66,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			}
 		}
 
-		public IndexerExpression(Expression target, params Expression[] arguments) : this(target, (IEnumerable<Expression>)arguments)
+		public IndexerExpression(Expression target, params Expression[]? arguments) : this(target, (IEnumerable<Expression>?)arguments)
 		{
 		}
 
@@ -85,9 +85,9 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return visitor.VisitIndexerExpression(this, data);
 		}
 
-		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
+		protected internal override bool DoMatch(AstNode? other, PatternMatching.Match match)
 		{
-			IndexerExpression o = other as IndexerExpression;
+			IndexerExpression? o = other as IndexerExpression;
 			return o != null && this.Target.DoMatch(o.Target, match) && this.Arguments.DoMatch(o.Arguments, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/InterpolatedStringExpression.cs

@@ -42,7 +42,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, Match match)
 		{
-			InterpolatedStringExpression o = other as InterpolatedStringExpression;
+			InterpolatedStringExpression? o = other as InterpolatedStringExpression;
 			return o != null && !o.IsNull && this.Content.DoMatch(o.Content, match);
 		}
 	}
@@ -117,7 +117,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		}
 
-		public Interpolation(Expression expression, int alignment = 0, string suffix = null)
+		public Interpolation(Expression expression, int alignment = 0, string? suffix = null)
 		{
 			Expression = expression;
 			Alignment = alignment;
@@ -141,7 +141,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, Match match)
 		{
-			Interpolation o = other as Interpolation;
+			Interpolation? o = other as Interpolation;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}
@@ -177,7 +177,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, Match match)
 		{
-			InterpolatedStringText o = other as InterpolatedStringText;
+			InterpolatedStringText? o = other as InterpolatedStringText;
 			return o != null && o.Text == this.Text;
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/InvocationExpression.cs

@@ -87,7 +87,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			InvocationExpression o = other as InvocationExpression;
+			InvocationExpression? o = other as InvocationExpression;
 			return o != null && this.Target.DoMatch(o.Target, match) && this.Arguments.DoMatch(o.Arguments, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/IsExpression.cs

@@ -76,7 +76,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			IsExpression o = other as IsExpression;
+			IsExpression? o = other as IsExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match) && this.Type.DoMatch(o.Type, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/LambdaExpression.cs

@@ -84,7 +84,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			LambdaExpression o = other as LambdaExpression;
+			LambdaExpression? o = other as LambdaExpression;
 			return o != null && this.IsAsync == o.IsAsync && this.Parameters.DoMatch(o.Parameters, match) && this.Body.DoMatch(o.Body, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/MemberReferenceExpression.cs

@@ -80,7 +80,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public MemberReferenceExpression(Expression target, string memberName, IEnumerable<AstType> arguments = null)
+		public MemberReferenceExpression(Expression target, string memberName, IEnumerable<AstType>? arguments = null)
 		{
 			AddChild(target, Roles.TargetExpression);
 			MemberName = memberName;
@@ -114,7 +114,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			MemberReferenceExpression o = other as MemberReferenceExpression;
+			MemberReferenceExpression? o = other as MemberReferenceExpression;
 			return o != null && this.Target.DoMatch(o.Target, match) && MatchString(this.MemberName, o.MemberName) && this.TypeArguments.DoMatch(o.TypeArguments, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/NamedArgumentExpression.cs

@@ -79,7 +79,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			NamedArgumentExpression o = other as NamedArgumentExpression;
+			NamedArgumentExpression? o = other as NamedArgumentExpression;
 			return o != null && MatchString(this.Name, o.Name) && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/NullReferenceExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			NullReferenceExpression o = other as NullReferenceExpression;
+			NullReferenceExpression? o = other as NullReferenceExpression;
 			return o != null;
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ObjectCreateExpression.cs

@@ -66,7 +66,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public ObjectCreateExpression(AstType type, IEnumerable<Expression> arguments = null)
+		public ObjectCreateExpression(AstType type, IEnumerable<Expression>? arguments = null)
 		{
 			AddChild(type, Roles.Type);
 			if (arguments != null)
@@ -99,7 +99,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ObjectCreateExpression o = other as ObjectCreateExpression;
+			ObjectCreateExpression? o = other as ObjectCreateExpression;
 			return o != null && this.Type.DoMatch(o.Type, match) && this.Arguments.DoMatch(o.Arguments, match) && this.Initializer.DoMatch(o.Initializer, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ParenthesizedExpression.cs

@@ -71,7 +71,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ParenthesizedExpression o = other as ParenthesizedExpression;
+			ParenthesizedExpression? o = other as ParenthesizedExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/PointerReferenceExpression.cs

@@ -82,7 +82,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			PointerReferenceExpression o = other as PointerReferenceExpression;
+			PointerReferenceExpression? o = other as PointerReferenceExpression;
 			return o != null && MatchString(this.MemberName, o.MemberName) && this.TypeArguments.DoMatch(o.TypeArguments, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/PrimitiveExpression.cs

@@ -145,7 +145,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			PrimitiveExpression o = other as PrimitiveExpression;
+			PrimitiveExpression? o = other as PrimitiveExpression;
 			return o != null && (this.Value == AnyValue || object.Equals(this.Value, o.Value));
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/QueryExpression.cs

@@ -76,7 +76,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryExpression o = other as QueryExpression;
+			QueryExpression? o = other as QueryExpression;
 			return o != null && !o.IsNull && this.Clauses.DoMatch(o.Clauses, match);
 		}
 	}
@@ -150,7 +150,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryContinuationClause o = other as QueryContinuationClause;
+			QueryContinuationClause? o = other as QueryContinuationClause;
 			return o != null && MatchString(this.Identifier, o.Identifier) && this.PrecedingQuery.DoMatch(o.PrecedingQuery, match);
 		}
 	}
@@ -208,7 +208,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryFromClause o = other as QueryFromClause;
+			QueryFromClause? o = other as QueryFromClause;
 			return o != null && this.Type.DoMatch(o.Type, match) && MatchString(this.Identifier, o.Identifier)
 				&& this.Expression.DoMatch(o.Expression, match);
 		}
@@ -261,7 +261,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryLetClause o = other as QueryLetClause;
+			QueryLetClause? o = other as QueryLetClause;
 			return o != null && MatchString(this.Identifier, o.Identifier) && this.Expression.DoMatch(o.Expression, match);
 		}
 	}
@@ -297,7 +297,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryWhereClause o = other as QueryWhereClause;
+			QueryWhereClause? o = other as QueryWhereClause;
 			return o != null && this.Condition.DoMatch(o.Condition, match);
 		}
 	}
@@ -406,7 +406,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryJoinClause o = other as QueryJoinClause;
+			QueryJoinClause? o = other as QueryJoinClause;
 			return o != null && this.IsGroupJoin == o.IsGroupJoin
 				&& this.Type.DoMatch(o.Type, match) && MatchString(this.JoinIdentifier, o.JoinIdentifier)
 				&& this.InExpression.DoMatch(o.InExpression, match) && this.OnExpression.DoMatch(o.OnExpression, match)
@@ -445,7 +445,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryOrderClause o = other as QueryOrderClause;
+			QueryOrderClause? o = other as QueryOrderClause;
 			return o != null && this.Orderings.DoMatch(o.Orderings, match);
 		}
 	}
@@ -490,7 +490,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryOrdering o = other as QueryOrdering;
+			QueryOrdering? o = other as QueryOrdering;
 			return o != null && this.Direction == o.Direction && this.Expression.DoMatch(o.Expression, match);
 		}
 	}
@@ -532,7 +532,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QuerySelectClause o = other as QuerySelectClause;
+			QuerySelectClause? o = other as QuerySelectClause;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}
@@ -579,7 +579,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			QueryGroupClause o = other as QueryGroupClause;
+			QueryGroupClause? o = other as QueryGroupClause;
 			return o != null && this.Projection.DoMatch(o.Projection, match) && this.Key.DoMatch(o.Key, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/SizeOfExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			SizeOfExpression o = other as SizeOfExpression;
+			SizeOfExpression? o = other as SizeOfExpression;
 			return o != null && this.Type.DoMatch(o.Type, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/StackAllocExpression.cs

@@ -79,7 +79,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			StackAllocExpression o = other as StackAllocExpression;
+			StackAllocExpression? o = other as StackAllocExpression;
 			return o != null && this.Type.DoMatch(o.Type, match)
 				&& this.CountExpression.DoMatch(o.CountExpression, match)
 				&& this.Initializer.DoMatch(o.Initializer, match);

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/SwitchExpression.cs

@@ -65,7 +65,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			SwitchExpression o = other as SwitchExpression;
+			SwitchExpression? o = other as SwitchExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match) && this.SwitchSections.DoMatch(o.SwitchSections, match);
 		}
 	}
@@ -111,7 +111,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			SwitchExpressionSection o = other as SwitchExpressionSection;
+			SwitchExpressionSection? o = other as SwitchExpressionSection;
 			return o != null && this.Pattern.DoMatch(o.Pattern, match) && this.Body.DoMatch(o.Body, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ThisReferenceExpression.cs

@@ -65,7 +65,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ThisReferenceExpression o = other as ThisReferenceExpression;
+			ThisReferenceExpression? o = other as ThisReferenceExpression;
 			return o != null;
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ThrowExpression.cs

@@ -60,7 +60,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ThrowExpression o = other as ThrowExpression;
+			ThrowExpression? o = other as ThrowExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/TypeOfExpression.cs

@@ -78,7 +78,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			TypeOfExpression o = other as TypeOfExpression;
+			TypeOfExpression? o = other as TypeOfExpression;
 			return o != null && this.Type.DoMatch(o.Type, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/TypeReferenceExpression.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			TypeReferenceExpression o = other as TypeReferenceExpression;
+			TypeReferenceExpression? o = other as TypeReferenceExpression;
 			return o != null && this.Type.DoMatch(o.Type, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/UnaryOperatorExpression.cs

@@ -89,7 +89,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			UnaryOperatorExpression o = other as UnaryOperatorExpression;
+			UnaryOperatorExpression? o = other as UnaryOperatorExpression;
 			return o != null && (this.Operator == UnaryOperatorType.Any || this.Operator == o.Operator)
 				&& this.Expression.DoMatch(o.Expression, match);
 		}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/UncheckedExpression.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			UncheckedExpression o = other as UncheckedExpression;
+			UncheckedExpression? o = other as UncheckedExpression;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/UndocumentedExpression.cs

@@ -97,7 +97,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			UndocumentedExpression o = other as UndocumentedExpression;
+			UndocumentedExpression? o = other as UndocumentedExpression;
 			return o != null && this.UndocumentedExpressionType == o.UndocumentedExpressionType && this.Arguments.DoMatch(o.Arguments, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/FunctionPointerAstType.cs

@@ -74,7 +74,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				&& this.ReturnType.DoMatch(o.ReturnType, match);
 		}
 
-		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null)
+		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null)
 		{
 			throw new NotImplementedException();
 		}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/Attribute.cs

@@ -79,7 +79,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			Attribute o = other as Attribute;
+			Attribute? o = other as Attribute;
 			return o != null && this.Type.DoMatch(o.Type, match) && this.Arguments.DoMatch(o.Arguments, match);
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/AttributeSection.cs

@@ -131,7 +131,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			AttributeSection o = other as AttributeSection;
+			AttributeSection? o = other as AttributeSection;
 			return o != null && MatchString(this.AttributeTarget, o.AttributeTarget) && this.Attributes.DoMatch(o.Attributes, match);
 		}
 

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/Comment.cs

@@ -145,7 +145,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			Comment o = other as Comment;
+			Comment? o = other as Comment;
 			return o != null && this.CommentType == o.CommentType && MatchString(this.Content, o.Content);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/Constraint.cs

@@ -75,7 +75,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			Constraint o = other as Constraint;
+			Constraint? o = other as Constraint;
 			return o != null && this.TypeParameter.DoMatch(o.TypeParameter, match) && this.BaseTypes.DoMatch(o.BaseTypes, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/DelegateDeclaration.cs

@@ -82,7 +82,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			DelegateDeclaration o = other as DelegateDeclaration;
+			DelegateDeclaration? o = other as DelegateDeclaration;
 			return o != null && MatchString(this.Name, o.Name)
 				&& this.MatchAttributesAndModifiers(o, match) && this.ReturnType.DoMatch(o.ReturnType, match)
 				&& this.TypeParameters.DoMatch(o.TypeParameters, match) && this.Parameters.DoMatch(o.Parameters, match)

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/NamespaceDeclaration.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// </summary>
 		public string FullName {
 			get {
-				NamespaceDeclaration parentNamespace = Parent as NamespaceDeclaration;
+				NamespaceDeclaration? parentNamespace = Parent as NamespaceDeclaration;
 				if (parentNamespace != null)
 					return BuildQualifiedName(parentNamespace.FullName, Name);
 				return Name;
@@ -152,7 +152,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			NamespaceDeclaration o = other as NamespaceDeclaration;
+			NamespaceDeclaration? o = other as NamespaceDeclaration;
 			return o != null && MatchString(this.Name, o.Name) && this.Members.DoMatch(o.Members, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/PreProcessorDirective.cs

@@ -62,7 +62,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public LinePreprocessorDirective(string argument = null) : base(PreProcessorDirectiveType.Line, argument)
+		public LinePreprocessorDirective(string? argument = null) : base(PreProcessorDirectiveType.Line, argument)
 		{
 		}
 	}
@@ -115,7 +115,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public PragmaWarningPreprocessorDirective(string argument = null) : base(PreProcessorDirectiveType.Pragma, argument)
+		public PragmaWarningPreprocessorDirective(string? argument = null) : base(PreProcessorDirectiveType.Pragma, argument)
 		{
 		}
 
@@ -172,7 +172,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			this.endLocation = endLocation;
 		}
 
-		public PreProcessorDirective(PreProcessorDirectiveType type, string argument = null)
+		public PreProcessorDirective(PreProcessorDirectiveType type, string? argument = null)
 		{
 			this.Type = type;
 			this.Argument = argument;
@@ -195,7 +195,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			PreProcessorDirective o = other as PreProcessorDirective;
+			PreProcessorDirective? o = other as PreProcessorDirective;
 			return o != null && Type == o.Type && MatchString(Argument, o.Argument);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/TypeDeclaration.cs

@@ -149,7 +149,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			TypeDeclaration o = other as TypeDeclaration;
+			TypeDeclaration? o = other as TypeDeclaration;
 			return o != null && this.ClassType == o.ClassType && MatchString(this.Name, o.Name)
 				&& this.MatchAttributesAndModifiers(o, match) && this.TypeParameters.DoMatch(o.TypeParameters, match)
 				&& this.BaseTypes.DoMatch(o.BaseTypes, match) && this.Constraints.DoMatch(o.Constraints, match)

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/TypeParameterDeclaration.cs

@@ -106,7 +106,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			TypeParameterDeclaration o = other as TypeParameterDeclaration;
+			TypeParameterDeclaration? o = other as TypeParameterDeclaration;
 			return o != null && this.Variance == o.Variance && MatchString(this.Name, o.Name) && this.Attributes.DoMatch(o.Attributes, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/UsingAliasDeclaration.cs

@@ -101,7 +101,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			UsingAliasDeclaration o = other as UsingAliasDeclaration;
+			UsingAliasDeclaration? o = other as UsingAliasDeclaration;
 			return o != null && MatchString(this.Alias, o.Alias) && this.Import.DoMatch(o.Import, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/GeneralScope/UsingDeclaration.cs

@@ -117,7 +117,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			UsingDeclaration o = other as UsingDeclaration;
+			UsingDeclaration? o = other as UsingDeclaration;
 			return o != null && this.Import.DoMatch(o.Import, match);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/IAnnotatable.cs

@@ -101,7 +101,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		/// </summary>
 		protected void CloneAnnotations()
 		{
-			ICloneable cloneable = annotations as ICloneable;
+			ICloneable? cloneable = annotations as ICloneable;
 			if (cloneable != null)
 				annotations = cloneable.Clone();
 		}
@@ -123,7 +123,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 					for (int i = 0; i < this.Count; i++)
 					{
 						object obj = this[i];
-						ICloneable c = obj as ICloneable;
+						ICloneable? c = obj as ICloneable;
 						copy.Add(c != null ? c.Clone() : obj);
 					}
 					return copy;
@@ -141,7 +141,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			{
 				return; // we successfully added a single annotation
 			}
-			AnnotationList list = oldAnnotation as AnnotationList;
+			AnnotationList? list = oldAnnotation as AnnotationList;
 			if (list == null)
 			{
 				// we need to transform the old annotation into a list
@@ -168,7 +168,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 			retry: // Retry until successful
 			object oldAnnotations = this.annotations;
-			AnnotationList list = oldAnnotations as AnnotationList;
+			AnnotationList? list = oldAnnotations as AnnotationList;
 			if (list != null)
 			{
 				lock (list)
@@ -190,7 +190,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				throw new ArgumentNullException(nameof(type));
 			retry: // Retry until successful
 			object oldAnnotations = this.annotations;
-			AnnotationList list = oldAnnotations as AnnotationList;
+			AnnotationList? list = oldAnnotations as AnnotationList;
 			if (list != null)
 			{
 				lock (list)
@@ -209,14 +209,14 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public T Annotation<T>() where T : class
 		{
 			object annotations = this.annotations;
-			AnnotationList list = annotations as AnnotationList;
+			AnnotationList? list = annotations as AnnotationList;
 			if (list != null)
 			{
 				lock (list)
 				{
 					foreach (object obj in list)
 					{
-						T t = obj as T;
+						T? t = obj as T;
 						if (t != null)
 							return t;
 					}
@@ -234,7 +234,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			if (type == null)
 				throw new ArgumentNullException(nameof(type));
 			object annotations = this.annotations;
-			AnnotationList list = annotations as AnnotationList;
+			AnnotationList? list = annotations as AnnotationList;
 			if (list != null)
 			{
 				lock (list)
@@ -260,7 +260,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public IEnumerable<object> Annotations {
 			get {
 				object annotations = this.annotations;
-				AnnotationList list = annotations as AnnotationList;
+				AnnotationList? list = annotations as AnnotationList;
 				if (list != null)
 				{
 					lock (list)

ICSharpCode.Decompiler/CSharp/Syntax/Identifier.cs

@@ -166,7 +166,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			Identifier o = other as Identifier;
+			Identifier? o = other as Identifier;
 			return o != null && !o.IsNull && MatchString(this.Name, o.Name);
 		}
 	}

ICSharpCode.Decompiler/CSharp/Syntax/IdentifierExpressionBackreference.cs

@@ -41,7 +41,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		public override bool DoMatch(PatternMatching.INode other, PatternMatching.Match match)
 		{
-			IdentifierExpression ident = other as IdentifierExpression;
+			IdentifierExpression? ident = other as IdentifierExpression;
 			if (ident == null || ident.TypeArguments.Any())
 				return false;
 			AstNode referenced = (AstNode)match.Get(referencedGroupName).Last();

ICSharpCode.Decompiler/CSharp/Syntax/InvocationAstType.cs

@@ -62,7 +62,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 				&& this.Arguments.DoMatch(o.Arguments, match);
 		}
 
-		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null)
+		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null)
 		{
 			throw new NotImplementedException();
 		}

ICSharpCode.Decompiler/CSharp/Syntax/MemberType.cs

@@ -114,21 +114,21 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			MemberType o = other as MemberType;
+			MemberType? o = other as MemberType;
 			return o != null && this.IsDoubleColon == o.IsDoubleColon
 				&& MatchString(this.MemberName, o.MemberName) && this.Target.DoMatch(o.Target, match)
 				&& this.TypeArguments.DoMatch(o.TypeArguments, match);
 		}
 
-		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null)
+		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null)
 		{
 			if (interningProvider == null)
 				interningProvider = InterningProvider.Dummy;
 
-			TypeOrNamespaceReference t;
+			TypeOrNamespaceReference? t;
 			if (this.IsDoubleColon)
 			{
-				SimpleType st = this.Target as SimpleType;
+				SimpleType? st = this.Target as SimpleType;
 				if (st != null)
 				{
 					t = interningProvider.Intern(new AliasNamespaceReference(interningProvider.Intern(st.Identifier)));

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

@@ -31,7 +31,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 			get { return groupName; }
 		}
 
-		public AnyNode(string groupName = null)
+		public AnyNode(string? groupName = null)
 		{
 			this.groupName = groupName;
 		}

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

@@ -39,7 +39,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching
 			get { return groupName; }
 		}
 
-		public AnyNodeOrNull(string groupName = null)
+		public AnyNodeOrNull(string? groupName = null)
 		{
 			this.groupName = groupName;
 		}

ICSharpCode.Decompiler/CSharp/Syntax/PrimitiveType.cs

@@ -102,7 +102,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			PrimitiveType o = other as PrimitiveType;
+			PrimitiveType? o = other as PrimitiveType;
 			return o != null && MatchString(this.Keyword, o.Keyword);
 		}
 
@@ -111,7 +111,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return Keyword;
 		}
 
-		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null)
+		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null)
 		{
 			KnownTypeCode typeCode = GetTypeCodeForPrimitiveType(this.Keyword);
 			if (typeCode == KnownTypeCode.None)

ICSharpCode.Decompiler/CSharp/Syntax/SimpleType.cs

@@ -143,11 +143,11 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			SimpleType o = other as SimpleType;
+			SimpleType? o = other as SimpleType;
 			return o != null && MatchString(this.Identifier, o.Identifier) && this.TypeArguments.DoMatch(o.TypeArguments, match);
 		}
 
-		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider interningProvider = null)
+		public override ITypeReference ToTypeReference(NameLookupMode lookupMode, InterningProvider? interningProvider = null)
 		{
 			if (interningProvider == null)
 				interningProvider = InterningProvider.Dummy;

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

@@ -142,7 +142,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			BlockStatement o = other as BlockStatement;
+			BlockStatement? o = other as BlockStatement;
 			return o != null && !o.IsNull && this.Statements.DoMatch(o.Statements, match);
 		}
 

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

@@ -59,7 +59,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			BreakStatement o = other as BreakStatement;
+			BreakStatement? o = other as BreakStatement;
 			return o != null;
 		}
 	}

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

@@ -69,7 +69,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			CheckedStatement o = other as CheckedStatement;
+			CheckedStatement? o = other as CheckedStatement;
 			return o != null && this.Body.DoMatch(o.Body, match);
 		}
 	}

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

@@ -59,7 +59,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ContinueStatement o = other as ContinueStatement;
+			ContinueStatement? o = other as ContinueStatement;
 			return o != null;
 		}
 	}

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

@@ -82,7 +82,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			DoWhileStatement o = other as DoWhileStatement;
+			DoWhileStatement? o = other as DoWhileStatement;
 			return o != null && this.EmbeddedStatement.DoMatch(o.EmbeddedStatement, match) && this.Condition.DoMatch(o.Condition, match);
 		}
 

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

@@ -66,7 +66,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			EmptyStatement o = other as EmptyStatement;
+			EmptyStatement? o = other as EmptyStatement;
 			return o != null;
 		}
 	}

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

@@ -67,7 +67,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ExpressionStatement o = other as ExpressionStatement;
+			ExpressionStatement? o = other as ExpressionStatement;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

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

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			FixedStatement o = other as FixedStatement;
+			FixedStatement? o = other as FixedStatement;
 			return o != null && this.Type.DoMatch(o.Type, match) && this.Variables.DoMatch(o.Variables, match) && this.EmbeddedStatement.DoMatch(o.EmbeddedStatement, match);
 		}
 	}

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

@@ -88,7 +88,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ForStatement o = other as ForStatement;
+			ForStatement? o = other as ForStatement;
 			return o != null && this.Initializers.DoMatch(o.Initializers, match) && this.Condition.DoMatch(o.Condition, match)
 				&& this.Iterators.DoMatch(o.Iterators, match) && this.EmbeddedStatement.DoMatch(o.EmbeddedStatement, match);
 		}

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

@@ -98,7 +98,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ForeachStatement o = other as ForeachStatement;
+			ForeachStatement? o = other as ForeachStatement;
 			return o != null && this.VariableType.DoMatch(o.VariableType, match) && this.VariableDesignation.DoMatch(o.VariableDesignation, match)
 				&& this.InExpression.DoMatch(o.InExpression, match) && this.EmbeddedStatement.DoMatch(o.EmbeddedStatement, match);
 		}

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

@@ -80,7 +80,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			GotoStatement o = other as GotoStatement;
+			GotoStatement? o = other as GotoStatement;
 			return o != null && MatchString(this.Label, o.Label);
 		}
 	}
@@ -130,7 +130,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			GotoCaseStatement o = other as GotoCaseStatement;
+			GotoCaseStatement? o = other as GotoCaseStatement;
 			return o != null && this.LabelExpression.DoMatch(o.LabelExpression, match);
 		}
 	}
@@ -172,7 +172,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			GotoDefaultStatement o = other as GotoDefaultStatement;
+			GotoDefaultStatement? o = other as GotoDefaultStatement;
 			return o != null;
 		}
 	}

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

@@ -86,7 +86,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			IfElseStatement o = other as IfElseStatement;
+			IfElseStatement? o = other as IfElseStatement;
 			return o != null && this.Condition.DoMatch(o.Condition, match) && this.TrueStatement.DoMatch(o.TrueStatement, match) && this.FalseStatement.DoMatch(o.FalseStatement, match);
 		}
 
@@ -94,7 +94,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		{
 		}
 
-		public IfElseStatement(Expression condition, Statement trueStatement, Statement falseStatement = null)
+		public IfElseStatement(Expression condition, Statement trueStatement, Statement? falseStatement = null)
 		{
 			this.Condition = condition;
 			this.TrueStatement = trueStatement;

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

@@ -67,7 +67,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			LabelStatement o = other as LabelStatement;
+			LabelStatement? o = other as LabelStatement;
 			return o != null && MatchString(this.Label, o.Label);
 		}
 	}

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

@@ -73,7 +73,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			LockStatement o = other as LockStatement;
+			LockStatement? o = other as LockStatement;
 			return o != null && this.Expression.DoMatch(o.Expression, match) && this.EmbeddedStatement.DoMatch(o.EmbeddedStatement, match);
 		}
 	}

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

@@ -73,7 +73,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			ReturnStatement o = other as ReturnStatement;
+			ReturnStatement? o = other as ReturnStatement;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}

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

@@ -81,7 +81,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			SwitchStatement o = other as SwitchStatement;
+			SwitchStatement? o = other as SwitchStatement;
 			return o != null && this.Expression.DoMatch(o.Expression, match) && this.SwitchSections.DoMatch(o.SwitchSections, match);
 		}
 	}
@@ -167,7 +167,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			SwitchSection o = other as SwitchSection;
+			SwitchSection? o = other as SwitchSection;
 			return o != null && this.CaseLabels.DoMatch(o.CaseLabels, match) && this.Statements.DoMatch(o.Statements, match);
 		}
 	}
@@ -221,7 +221,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 
 		protected internal override bool DoMatch(AstNode other, PatternMatching.Match match)
 		{
-			CaseLabel o = other as CaseLabel;
+			CaseLabel? o = other as CaseLabel;
 			return o != null && this.Expression.DoMatch(o.Expression, match);
 		}
 	}