more CS8600 cleanup

ICSharpCode.BamlDecompiler/Baml/BamlContext.cs

@@ -116,7 +116,7 @@ namespace ICSharpCode.BamlDecompiler.Baml
 
 		private IModule FindMatchingReference(AssemblyNameReference name)
 		{
-			IModule bestMatch = null;
+			IModule? bestMatch = null;
 			foreach (var module in TypeSystem.ReferencedModules)
 			{
 				if (module.AssemblyName == name.Name)

ICSharpCode.BamlDecompiler/Baml/BamlNode.cs

@@ -111,7 +111,7 @@ namespace ICSharpCode.BamlDecompiler.Baml
 		{
 			Debug.Assert(document.Count > 0 && document[0].Type == BamlRecordType.DocumentStart);
 
-			BamlBlockNode current = null;
+			BamlBlockNode? current = null;
 			var stack = new Stack<BamlBlockNode>();
 
 			for (int i = 0; i < document.Count; i++)

ICSharpCode.BamlDecompiler/Baml/BamlReader.cs

@@ -91,7 +91,7 @@ namespace ICSharpCode.BamlDecompiler.Baml
 
 				long pos = str.Position;
 				var type = (BamlRecordType)reader.ReadByte();
-				BamlRecord rec = null;
+				BamlRecord? rec = null;
 				switch (type)
 				{
 					case BamlRecordType.AssemblyInfo:

ICSharpCode.BamlDecompiler/Rewrite/ConnectionIdRewritePass.cs

@@ -127,7 +127,7 @@ namespace ICSharpCode.BamlDecompiler.Rewrite
 				return;
 			var connect = connectorInterface.GetMethods(m => m.Name == "Connect").SingleOrDefault();
 
-			IMethod connectMethod = null;
+			IMethod? connectMethod = null;
 			MethodDefinition connectMetadataEntry = default;
 			var module = ctx.TypeSystem.MainModule.MetadataFile;
 

ICSharpCode.BamlDecompiler/Xaml/XamlType.cs

@@ -62,7 +62,7 @@ namespace ICSharpCode.BamlDecompiler.Xaml
 			// Since XmlnsProperty records are inside the element,
 			// the namespace is resolved after processing the element body.
 
-			string xmlNs = null;
+			string? xmlNs = null;
 			if (elem.Annotation<XmlnsScope>() != null)
 				xmlNs = elem.Annotation<XmlnsScope>().LookupXmlns(FullAssemblyName, TypeNamespace);
 			if (xmlNs == null)

ICSharpCode.BamlDecompiler/XamlContext.cs

@@ -143,7 +143,7 @@ namespace ICSharpCode.BamlDecompiler
 
 			XamlType type;
 			string name;
-			IMember member;
+			IMember? member;
 
 			if (id > 0x7fff)
 			{

ICSharpCode.Decompiler/CSharp/OutputVisitor/TextWriterTokenWriter.cs

@@ -499,7 +499,7 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			StringBuilder sb = new StringBuilder();
 			foreach (char ch in str)
 			{
-				string s = ch == '"' ? "\\\"" : ConvertChar(ch);
+				string? s = ch == '"' ? "\\\"" : ConvertChar(ch);
 				if (s != null)
 					sb.Append(s);
 				else

ICSharpCode.Decompiler/Util/CSharpPrimitiveCast.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace ICSharpCode.Decompiler.Util
 {
@@ -34,7 +35,9 @@ namespace ICSharpCode.Decompiler.Util
 		/// </summary>
 		/// <exception cref="OverflowException">Overflow checking is enabled and an overflow occurred.</exception>
 		/// <exception cref="InvalidCastException">The cast is invalid, e.g. casting a boolean to an integer.</exception>
-		public static object? Cast(TypeCode targetType, object input, bool checkForOverflow)
+		//[return: MaybeNull]
+		//[return: NotNullIfNotNull(nameof(input))]
+		public static object Cast(TypeCode targetType, [MaybeNull] object input, bool checkForOverflow)
 		{
 			if (input == null)
 				return null;

ICSharpCode.ILSpyCmd/IlspyCmdProgram.cs

@@ -122,7 +122,7 @@ Examples:
 
 		private async Task<int> OnExecuteAsync(CommandLineApplication app)
 		{
-			Task<PackageCheckResult> updateCheckTask = null;
+			Task<PackageCheckResult>? updateCheckTask = null;
 			if (!DisableUpdateCheck)
 			{
 				updateCheckTask = DotNetToolUpdateChecker.CheckForPackageUpdateAsync("ilspycmd");
@@ -214,7 +214,7 @@ Examples:
 				}
 				else if (CreateDebugInfoFlag)
 				{
-					string pdbFileName = null;
+					string? pdbFileName = null;
 					if (outputDirectory != null)
 					{
 						string outputName = Path.GetFileNameWithoutExtension(fileName);

ILSpy.BamlDecompiler.Tests/BamlTestRunner.cs

@@ -205,11 +205,11 @@ namespace ILSpy.BamlDecompiler.Tests
 			return line.Trim();
 		}
 
-		Stream LoadBaml(Resource res, string name)
+		Stream? LoadBaml(Resource res, string name)
 		{
 			if (res.ResourceType != ResourceType.Embedded)
 				return null;
-			Stream s = res.TryOpenStream();
+			Stream? s = res.TryOpenStream();
 			if (s == null)
 				return null;
 			s.Position = 0;

ILSpy.ReadyToRun/ReadyToRunDisassembler.cs

@@ -67,14 +67,14 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 				}
 			}
 
-			Dictionary<ulong, UnwindCode> unwindInfo = null;
+			Dictionary<ulong, UnwindCode>? unwindInfo = null;
 			if (ReadyToRunOptions.GetIsShowUnwindInfo(null) && bitness == 64)
 			{
 				unwindInfo = WriteUnwindInfo();
 			}
 
 			bool isShowDebugInfo = ReadyToRunOptions.GetIsShowDebugInfo(null);
-			DebugInfoHelper debugInfo = null;
+			DebugInfoHelper? debugInfo = null;
 			if (isShowDebugInfo)
 			{
 				debugInfo = WriteDebugInfo();
@@ -98,7 +98,7 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 			}
 
 			string disassemblyFormat = ReadyToRunOptions.GetDisassemblyFormat(null);
-			Formatter formatter = null;
+			Formatter? formatter = null;
 			if (disassemblyFormat.Equals(ReadyToRunOptions.intel))
 			{
 				formatter = new NasmFormatter();

ILSpy.ReadyToRun/ReadyToRunLanguage.cs

@@ -114,7 +114,7 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 
 		public override ProjectId DecompileAssembly(LoadedAssembly assembly, ITextOutput output, DecompilationOptions options)
 		{
-			PEFile module = assembly.GetMetadataFileAsync().GetAwaiter().GetResult() as PEFile;
+			PEFile? module = assembly.GetMetadataFileAsync().GetAwaiter().GetResult() as PEFile;
 			ReadyToRunReaderCacheEntry cacheEntry = GetReader(assembly, module);
 			if (cacheEntry.readyToRunReader == null)
 			{
@@ -137,7 +137,7 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 
 		public override void DecompileMethod(IMethod method, ITextOutput output, DecompilationOptions options)
 		{
-			PEFile module = method.ParentModule.MetadataFile as PEFile;
+			PEFile? module = method.ParentModule.MetadataFile as PEFile;
 			ReadyToRunReaderCacheEntry cacheEntry = GetReader(module.GetLoadedAssembly(), module);
 			if (cacheEntry.readyToRunReader == null)
 			{
@@ -158,7 +158,7 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 				}
 				if (cacheEntry.methodMap == null)
 				{
-					IEnumerable<ReadyToRunMethod> readyToRunMethods = null;
+					IEnumerable<ReadyToRunMethod>? readyToRunMethods = null;
 					if (cacheEntry.compositeReadyToRunReader == null)
 					{
 						readyToRunMethods = reader.Methods;
@@ -192,8 +192,8 @@ namespace ICSharpCode.ILSpy.ReadyToRun
 #endif
 						foreach (RuntimeFunction runtimeFunction in readyToRunMethod.RuntimeFunctions)
 						{
-							PEFile file = null;
-							ReadyToRunReader disassemblingReader = null;
+							PEFile? file = null;
+							ReadyToRunReader? disassemblingReader = null;
 							if (cacheEntry.compositeReadyToRunReader == null)
 							{
 								disassemblingReader = reader;

ILSpy/AboutPage.cs

@@ -90,11 +90,11 @@ namespace ICSharpCode.ILSpy
 				plugin.Write(output);
 			output.WriteLine();
 			output.Address = new Uri("resource://AboutPage");
-			using (Stream s = typeof(AboutPage).Assembly.GetManifestResourceStream(typeof(AboutPage), Resources.ILSpyAboutPageTxt))
+			using (Stream? s = typeof(AboutPage).Assembly.GetManifestResourceStream(typeof(AboutPage), Resources.ILSpyAboutPageTxt))
 			{
 				using (StreamReader r = new StreamReader(s))
 				{
-					string line;
+					string? line;
 					while ((line = r.ReadLine()) != null)
 					{
 						output.WriteLine(line);

ILSpy/Analyzers/AnalyzerEntityTreeNode.cs

@@ -54,7 +54,7 @@ namespace ICSharpCode.ILSpy.Analyzers
 			}
 			this.Children.RemoveAll(
 				delegate (SharpTreeNode n) {
-					AnalyzerTreeNode an = n as AnalyzerTreeNode;
+					AnalyzerTreeNode? an = n as AnalyzerTreeNode;
 					return an == null || !an.HandleAssemblyListChanged(removedAssemblies, addedAssemblies);
 				});
 			return true;

ILSpy/Analyzers/AnalyzerRootNode.cs

@@ -15,7 +15,7 @@ public sealed class AnalyzerRootNode : AnalyzerTreeNode
 		MessageBus<CurrentAssemblyListChangedEventArgs>.Subscribers += (sender, e) => CurrentAssemblyList_Changed(sender, e);
 	}
 
-	void CurrentAssemblyList_Changed(object sender, NotifyCollectionChangedEventArgs e)
+	void CurrentAssemblyList_Changed(object? sender, NotifyCollectionChangedEventArgs e)
 	{
 		if (e.Action == NotifyCollectionChangedAction.Reset)
 		{
@@ -34,7 +34,7 @@ public sealed class AnalyzerRootNode : AnalyzerTreeNode
 	{
 		this.Children.RemoveAll(
 			delegate (SharpTreeNode n) {
-				AnalyzerTreeNode an = n as AnalyzerTreeNode;
+				AnalyzerTreeNode? an = n as AnalyzerTreeNode;
 				return an == null || !an.HandleAssemblyListChanged(removedAssemblies, addedAssemblies);
 			});
 		return true;

ILSpy/Analyzers/AnalyzerTreeViewModel.cs

@@ -73,7 +73,7 @@ namespace ICSharpCode.ILSpy.Analyzers
 		{
 			Show();
 
-			AnalyzerTreeNode target = default;
+			AnalyzerTreeNode? target = default;
 
 			if (node is AnalyzerEntityTreeNode { Member: { } member })
 			{

ILSpy/App.xaml.cs

@@ -224,7 +224,7 @@ namespace ICSharpCode.ILSpy
 
 		static void ShowErrorBox(object sender, UnhandledExceptionEventArgs e)
 		{
-			Exception ex = e.ExceptionObject as Exception;
+			Exception? ex = e.ExceptionObject as Exception;
 			if (ex != null)
 			{
 				UnhandledException(ex);
@@ -237,13 +237,13 @@ namespace ICSharpCode.ILSpy
 		internal static void UnhandledException(Exception exception)
 		{
 			Debug.WriteLine(exception.ToString());
-			for (Exception ex = exception; ex != null; ex = ex.InnerException)
+			for (Exception? ex = exception; ex != null; ex = ex.InnerException)
 			{
-				ReflectionTypeLoadException rtle = ex as ReflectionTypeLoadException;
+				ReflectionTypeLoadException? rtle = ex as ReflectionTypeLoadException;
 				if (rtle != null && rtle.LoaderExceptions.Length > 0)
 				{
 					exception = rtle.LoaderExceptions[0];
-					Debug.WriteLine(exception.ToString());
+					Debug.WriteLine(exception?.ToString());
 					break;
 				}
 			}

ILSpy/AvalonEdit/TextMarkerService.cs

@@ -102,7 +102,7 @@ namespace ICSharpCode.ILSpy.AvalonEdit
 		{
 			if (marker == null)
 				throw new ArgumentNullException(nameof(marker));
-			TextMarker m = marker as TextMarker;
+			TextMarker? m = marker as TextMarker;
 			if (markers != null && markers.Remove(m))
 			{
 				Redraw(m);
@@ -131,7 +131,7 @@ namespace ICSharpCode.ILSpy.AvalonEdit
 			int lineEnd = lineStart + line.Length;
 			foreach (TextMarker marker in markers.FindOverlappingSegments(lineStart, line.Length))
 			{
-				Brush foregroundBrush = null;
+				Brush? foregroundBrush = null;
 				if (marker.ForegroundColor != null)
 				{
 					foregroundBrush = new SolidColorBrush(marker.ForegroundColor.Value);

ILSpy/Commands/CommandWrapper.cs

@@ -32,7 +32,7 @@ namespace ICSharpCode.ILSpy
 
 		public static ICommand Unwrap(ICommand command)
 		{
-			CommandWrapper w = command as CommandWrapper;
+			CommandWrapper? w = command as CommandWrapper;
 			if (w != null)
 				return w.wrappedCommand;
 			else

ILSpy/Commands/DecompileAllCommand.cs

@@ -55,7 +55,7 @@ namespace ICSharpCode.ILSpy
 						if (!asm.HasLoadError)
 						{
 							Stopwatch w = Stopwatch.StartNew();
-							Exception exception = null;
+							Exception? exception = null;
 							using (var writer = new System.IO.StreamWriter("c:\\temp\\decompiled\\" + asm.ShortName + ".cs"))
 							{
 								try

ILSpy/Commands/DecompileCommand.cs

@@ -56,7 +56,7 @@ namespace ICSharpCode.ILSpy.Commands
 
 		public void Execute(TextViewContext context)
 		{
-			IEntity selection = null;
+			IEntity? selection = null;
 			if (context.SelectedTreeNodes?[0] is IMemberTreeNode node)
 			{
 				selection = node.Member;

ILSpy/Commands/DisassembleAllCommand.cs

@@ -50,7 +50,7 @@ namespace ICSharpCode.ILSpy
 						if (!asm.HasLoadError)
 						{
 							Stopwatch w = Stopwatch.StartNew();
-							Exception exception = null;
+							Exception? exception = null;
 							using (var writer = new System.IO.StreamWriter("c:\\temp\\disassembled\\" + asm.Text.Replace("(", "").Replace(")", "").Replace(' ', '_') + ".il"))
 							{
 								try

ILSpy/Commands/ExtractPackageEntryContextMenuEntry.cs

@@ -57,7 +57,7 @@ namespace ICSharpCode.ILSpy
 				return;
 
 			string fileName = dlg.FileName;
-			string outputFolderOrFileName = fileName;
+			string? outputFolderOrFileName = fileName;
 			if (selectedNodes.Length > 1)
 				outputFolderOrFileName = Path.GetDirectoryName(outputFolderOrFileName);
 
@@ -89,7 +89,7 @@ namespace ICSharpCode.ILSpy
 		void SaveEntry(ITextOutput output, PackageEntry entry, string targetFileName)
 		{
 			output.Write(entry.Name + ": ");
-			using Stream stream = entry.TryOpenStream();
+			using Stream? stream = entry.TryOpenStream();
 			if (stream == null)
 			{
 				output.WriteLine("Could not open stream!");

ILSpy/Commands/SaveCodeContextMenuEntry.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.ComponentModel.Composition;
 using System.IO;
 using System.Linq;
 using System.Windows;
@@ -26,13 +27,11 @@ using ICSharpCode.Decompiler.IL;
 using ICSharpCode.ILSpy.Options;
 using ICSharpCode.ILSpy.Properties;
 using ICSharpCode.ILSpy.TreeNodes;
+using ICSharpCode.ILSpy.Util;
 using ICSharpCode.ILSpy.ViewModels;
-
-using Microsoft.Win32;
 using ICSharpCode.ILSpyX.TreeView;
-using System.ComponentModel.Composition;
 
-using ICSharpCode.ILSpy.Util;
+using Microsoft.Win32;
 
 namespace ICSharpCode.ILSpy.TextView
 {
@@ -112,7 +111,7 @@ namespace ICSharpCode.ILSpy.TextView
 				return null;
 			}
 
-			string selectedPath = Path.GetDirectoryName(dlg.FileName);
+			string? selectedPath = Path.GetDirectoryName(dlg.FileName);
 			bool directoryNotEmpty;
 			try
 			{

ILSpy/Commands/ScopeSearchToNamespace.cs

@@ -41,7 +41,7 @@ namespace ICSharpCode.ILSpy
 		public void Execute(TextViewContext context)
 		{
 			string ns = GetNamespace(context);
-			string searchTerm = searchPane.SearchTerm;
+			string? searchTerm = searchPane.SearchTerm;
 			string[] args = CommandLineTools.CommandLineToArgumentArray(searchTerm);
 			bool replaced = false;
 			for (int i = 0; i < args.Length; i++)

ILSpy/Commands/SelectPdbContextMenuEntry.cs

@@ -48,7 +48,7 @@ namespace ICSharpCode.ILSpy
 				await assembly.LoadDebugInfo(dlg.FileName);
 			}
 
-			var node = (AssemblyTreeNode)MainWindow.Instance.FindNodeByPath(new[] { assembly.FileName }, true);
+			var node = (AssemblyTreeNode?)MainWindow.Instance.FindNodeByPath(new[] { assembly.FileName }, true);
 			node.UpdateToolTip();
 			MainWindow.Instance.SelectNode(node);
 			MainWindow.Instance.RefreshDecompiledView();

ILSpy/ContextMenuEntry.cs

@@ -26,9 +26,9 @@ using System.Windows.Input;
 using System.Windows.Media;
 
 using ICSharpCode.AvalonEdit;
+using ICSharpCode.ILSpy.Controls.TreeView;
 using ICSharpCode.ILSpy.TextView;
 using ICSharpCode.ILSpyX.Search;
-using ICSharpCode.ILSpy.Controls.TreeView;
 using ICSharpCode.ILSpyX.TreeView;
 
 using TomsToolbox.Composition;
@@ -48,37 +48,37 @@ namespace ICSharpCode.ILSpy
 		/// Returns the selected nodes in the tree view.
 		/// Returns null, if context menu does not belong to a tree view.
 		/// </summary>
-		public SharpTreeNode[] SelectedTreeNodes { get; private set; }
+		public SharpTreeNode[]? SelectedTreeNodes { get; private set; }
 
 		/// <summary>
 		/// Returns the tree view the context menu is assigned to.
 		/// Returns null, if context menu is not assigned to a tree view.
 		/// </summary>
-		public SharpTreeView TreeView { get; private set; }
+		public SharpTreeView? TreeView { get; private set; }
 
 		/// <summary>
 		/// Returns the text view the context menu is assigned to.
 		/// Returns null, if context menu is not assigned to a text view.
 		/// </summary>
-		public DecompilerTextView TextView { get; private set; }
+		public DecompilerTextView? TextView { get; private set; }
 
 		/// <summary>
 		/// Returns the list box the context menu is assigned to.
 		/// Returns null, if context menu is not assigned to a list box.
 		/// </summary>
-		public ListBox ListBox { get; private set; }
+		public ListBox? ListBox { get; private set; }
 
 		/// <summary>
 		/// Returns the data grid the context menu is assigned to.
 		/// Returns null, if context menu is not assigned to a data grid.
 		/// </summary>
-		public DataGrid DataGrid { get; private set; }
+		public DataGrid? DataGrid { get; private set; }
 
 		/// <summary>
 		/// Returns the reference the mouse cursor is currently hovering above.
 		/// Returns null, if there was no reference found.
 		/// </summary>
-		public ReferenceSegment Reference { get; private set; }
+		public ReferenceSegment? Reference { get; private set; }
 
 		/// <summary>
 		/// Returns the position in TextView the mouse cursor is currently hovering above.
@@ -88,9 +88,9 @@ namespace ICSharpCode.ILSpy
 
 		public Point MousePosition { get; private set; }
 
-		public static TextViewContext Create(SharpTreeView treeView = null, DecompilerTextView textView = null, ListBox listBox = null, DataGrid dataGrid = null)
+		public static TextViewContext Create(SharpTreeView? treeView = null, DecompilerTextView? textView = null, ListBox? listBox = null, DataGrid? dataGrid = null)
 		{
-			ReferenceSegment reference;
+			ReferenceSegment? reference;
 			if (textView != null)
 				reference = textView.GetReferenceSegmentAtMousePosition();
 			else if (listBox?.SelectedItem is SearchResult result)
@@ -115,7 +115,7 @@ namespace ICSharpCode.ILSpy
 				TextView = textView,
 				Reference = reference,
 				Position = position,
-				MousePosition = ((Visual)textView ?? treeView ?? (Visual)listBox ?? dataGrid).PointToScreen(Mouse.GetPosition((IInputElement)textView ?? treeView ?? (IInputElement)listBox ?? dataGrid))
+				MousePosition = ((Visual?)textView ?? treeView ?? (Visual?)listBox ?? dataGrid).PointToScreen(Mouse.GetPosition((IInputElement?)textView ?? treeView ?? (IInputElement?)listBox ?? dataGrid))
 			};
 		}
 	}
@@ -291,7 +291,7 @@ namespace ICSharpCode.ILSpy
 		{
 			menu = new ContextMenu();
 			var menuGroups = new Dictionary<string, IExport<IContextMenuEntry, IContextMenuEntryMetadata>[]>();
-			IExport<IContextMenuEntry, IContextMenuEntryMetadata>[] topLevelGroup = null;
+			IExport<IContextMenuEntry, IContextMenuEntryMetadata>[]? topLevelGroup = null;
 			foreach (var group in entries.OrderBy(c => c.Metadata.Order).GroupBy(c => c.Metadata.ParentMenuID))
 			{
 				if (group.Key == null)
@@ -313,7 +313,7 @@ namespace ICSharpCode.ILSpy
 					bool needSeparatorForCategory = parent.Count > 0;
 					foreach (var entryPair in category)
 					{
-						IContextMenuEntry entry = entryPair.Value;
+						IContextMenuEntry? entry = entryPair.Value;
 						if (entry.IsVisible(context))
 						{
 							if (needSeparatorForCategory)

ILSpy/Controls/GridViewColumnAutoSize.cs

@@ -52,25 +52,25 @@ namespace ICSharpCode.ILSpy.Controls
 
 		static void AutoWidthPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
 		{
-			ListView grid = sender as ListView;
+			ListView? grid = sender as ListView;
 			if (grid == null)
 				return;
 			grid.SizeChanged += delegate (object listView, SizeChangedEventArgs e) {
-				ListView lv = listView as ListView;
+				ListView? lv = listView as ListView;
 				if (lv == null)
 					return;
-				GridView v = lv.View as GridView;
+				GridView? v = lv.View as GridView;
 				if (v == null)
 					return;
 				CalculateSizes(v, GetAutoWidth(lv), e.NewSize.Width);
 			};
-			GridView view = grid.View as GridView;
+			GridView? view = grid.View as GridView;
 			if (view == null)
 				return;
 			CalculateSizes(view, args.NewValue as string, grid.ActualWidth);
 		}
 
-		static void CalculateSizes(GridView view, string sizeValue, double fullWidth)
+		static void CalculateSizes(GridView view, string? sizeValue, double fullWidth)
 		{
 			string[] sizes = (sizeValue ?? "").Split(';');
 

ILSpy/Controls/SearchBox.cs

@@ -137,7 +137,7 @@ namespace ICSharpCode.ILSpy.Controls
 		{
 			base.OnApplyTemplate();
 
-			Border iconBorder = GetTemplateChild("PART_IconBorder") as Border;
+			Border? iconBorder = GetTemplateChild("PART_IconBorder") as Border;
 			if (iconBorder != null)
 			{
 				iconBorder.MouseLeftButtonUp += IconBorder_MouseLeftButtonUp;

ILSpy/Controls/SortableGridViewColumn.cs

@@ -73,7 +73,7 @@ namespace ICSharpCode.ILSpy.Controls
 
 		static void OnSortDirectionChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
 		{
-			ListView grid = sender as ListView;
+			ListView? grid = sender as ListView;
 			if (grid != null)
 			{
 				SortableGridViewColumn col = GetCurrentSortColumn(grid);
@@ -101,7 +101,7 @@ namespace ICSharpCode.ILSpy.Controls
 
 		static void OnCurrentSortColumnChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
 		{
-			ListView grid = sender as ListView;
+			ListView? grid = sender as ListView;
 			if (grid != null)
 			{
 				SortableGridViewColumn oldColumn = (SortableGridViewColumn)args.OldValue;
@@ -134,7 +134,7 @@ namespace ICSharpCode.ILSpy.Controls
 
 		static void OnSortModeChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
 		{
-			ListView grid = sender as ListView;
+			ListView? grid = sender as ListView;
 			if (grid != null)
 			{
 				if ((ListViewSortMode)args.NewValue != ListViewSortMode.None)
@@ -146,8 +146,8 @@ namespace ICSharpCode.ILSpy.Controls
 
 		static void GridViewColumnHeaderClickHandler(object sender, RoutedEventArgs e)
 		{
-			ListView grid = sender as ListView;
-			GridViewColumnHeader headerClicked = e.OriginalSource as GridViewColumnHeader;
+			ListView? grid = sender as ListView;
+			GridViewColumnHeader? headerClicked = e.OriginalSource as GridViewColumnHeader;
 			if (grid != null && headerClicked != null && headerClicked.Role != GridViewColumnHeaderRole.Padding)
 			{
 				if (headerClicked.Column == GetCurrentSortColumn(grid))
@@ -188,7 +188,7 @@ namespace ICSharpCode.ILSpy.Controls
 				string sortBy = column.SortBy;
 				if (sortBy == null)
 				{
-					Binding binding = column.DisplayMemberBinding as Binding;
+					Binding? binding = column.DisplayMemberBinding as Binding;
 					if (binding != null && binding.Path != null)
 					{
 						sortBy = binding.Path.Path;

ILSpy/Controls/TreeView/SharpTreeView.cs

@@ -176,8 +176,8 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 			// Deselect nodes that are being hidden, if any remain in the tree
 			if (e.Action == NotifyCollectionChangedAction.Remove && Items.Count > 0)
 			{
-				List<SharpTreeNode> selectedOldItems = null;
-				foreach (SharpTreeNode node in e.OldItems)
+				List<SharpTreeNode>? selectedOldItems = null;
+				foreach (SharpTreeNode node in e.OldItems!)
 				{
 					if (node.IsSelected)
 					{
@@ -194,7 +194,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 			}
 		}
 
-		void UpdateFocusedNode(List<SharpTreeNode> newSelection, int topSelectedIndex)
+		void UpdateFocusedNode(List<SharpTreeNode>? newSelection, int topSelectedIndex)
 		{
 			if (updatesLocked)
 				return;
@@ -222,7 +222,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 		protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
 		{
 			base.PrepareContainerForItemOverride(element, item);
-			SharpTreeViewItem container = element as SharpTreeViewItem;
+			SharpTreeViewItem? container = element as SharpTreeViewItem;
 			container.ParentTreeView = this;
 			// Make sure that the line renderer takes into account the new bound data
 			if (container.NodeView != null)
@@ -244,7 +244,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 			SharpTreeNode lastVisibleChild = node;
 			while (true)
 			{
-				SharpTreeNode tmp = lastVisibleChild.Children.LastOrDefault(c => c.IsVisible);
+				SharpTreeNode? tmp = lastVisibleChild.Children.LastOrDefault(c => c.IsVisible);
 				if (tmp != null)
 				{
 					lastVisibleChild = tmp;
@@ -269,7 +269,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 
 		protected override void OnKeyDown(KeyEventArgs e)
 		{
-			SharpTreeViewItem container = e.OriginalSource as SharpTreeViewItem;
+			SharpTreeViewItem? container = e.OriginalSource as SharpTreeViewItem;
 			switch (e.Key)
 			{
 				case Key.Left:
@@ -422,7 +422,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 
 		object? OnFocusItem(object item)
 		{
-			FrameworkElement element = this.ItemContainerGenerator.ContainerFromItem(item) as FrameworkElement;
+			FrameworkElement? element = this.ItemContainerGenerator.ContainerFromItem(item) as FrameworkElement;
 			if (element != null)
 			{
 				element.Focus();
@@ -606,7 +606,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 
 		void TryAddDropTarget(List<DropTarget> targets, SharpTreeViewItem item, DropPlace place, DragEventArgs e)
 		{
-			SharpTreeNode node;
+			SharpTreeNode? node;
 			int index;
 
 			GetNodeAndIndex(item, place, out node, out index);
@@ -627,7 +627,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 			}
 		}
 
-		void GetNodeAndIndex(SharpTreeViewItem item, DropPlace place, out SharpTreeNode node, out int index)
+		void GetNodeAndIndex(SharpTreeViewItem item, DropPlace place, out SharpTreeNode? node, out int index)
 		{
 			node = null;
 			index = 0;
@@ -697,7 +697,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 
 				insertMarker.Margin = new Thickness(p.X, p.Y, 0, 0);
 
-				SharpTreeNodeView secondNodeView = null;
+				SharpTreeNodeView? secondNodeView = null;
 				var index = flattener.IndexOf(item.Node);
 
 				if (place == DropPlace.Before)

ILSpy/Controls/TreeView/SharpTreeViewTextSearch.cs

@@ -116,7 +116,7 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 				var item = (SharpTreeNode)treeView.Items[i];
 				if (item != null && item.Text != null)
 				{
-					string text = item.Text.ToString();
+					string text = item.Text.ToString() ?? "";
 					if (text.StartsWith(needle, comparisonType))
 					{
 						charWasUsed = true;

ILSpy/Controls/ZoomScrollViewer.cs

@@ -103,7 +103,7 @@ namespace ICSharpCode.ILSpy.Controls
 
 		static void CalculateZoomButtonCollapsed(DependencyObject d, DependencyPropertyChangedEventArgs e)
 		{
-			ZoomScrollViewer z = d as ZoomScrollViewer;
+			ZoomScrollViewer? z = d as ZoomScrollViewer;
 			if (z != null)
 				z.ComputedZoomButtonCollapsed = (z.AlwaysShowZoomButtons == false) && (z.CurrentZoom == 1.0);
 		}
@@ -117,7 +117,7 @@ namespace ICSharpCode.ILSpy.Controls
 				newZoom = Math.Max(this.MinimumZoom, Math.Min(this.MaximumZoom, newZoom));
 
 				// adjust scroll position so that mouse stays over the same virtual coordinate
-				ContentPresenter presenter = Template.FindName("PART_Presenter", this) as ContentPresenter;
+				ContentPresenter? presenter = Template.FindName("PART_Presenter", this) as ContentPresenter;
 				Vector relMousePos;
 				if (presenter != null)
 				{

ILSpy/Docking/DockWorkspace.cs

@@ -84,7 +84,7 @@ namespace ICSharpCode.ILSpy.Docking
 
 		private void Documents_CollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
 		{
-			var collection = (PaneCollection<TabPageModel>)sender;
+			var collection = (PaneCollection<TabPageModel>?)sender;
 			if (e.Action == NotifyCollectionChangedAction.Add)
 			{
 				ActiveTabPage = e.NewItems?[0] as TabPageModel;
@@ -246,7 +246,7 @@ namespace ICSharpCode.ILSpy.Docking
 			{
 				var anchorable = layout.Descendents().OfType<LayoutAnchorable>().FirstOrDefault(x => x.Content is T)
 					?? layout.Hidden.First(x => x.Content is T);
-				return (LayoutAnchorablePane)previousContainerProperty.GetValue(anchorable) ?? (LayoutAnchorablePane)anchorable.Parent;
+				return (LayoutAnchorablePane?)previousContainerProperty.GetValue(anchorable) ?? (LayoutAnchorablePane)anchorable.Parent;
 			}
 		}
 

ILSpy/ISmartTextOutput.cs

@@ -52,7 +52,7 @@ namespace ICSharpCode.ILSpy
 		/// <summary>
 		/// Creates a button.
 		/// </summary>
-		public static void AddButton(this ISmartTextOutput output, ImageSource icon, string text, RoutedEventHandler click)
+		public static void AddButton(this ISmartTextOutput output, ImageSource? icon, string text, RoutedEventHandler click)
 		{
 			output.AddUIElement(
 				delegate {

ILSpy/Images/Images.cs

@@ -150,12 +150,12 @@ namespace ICSharpCode.ILSpy
 			return image;
 		}
 
-		public static Drawing LoadDrawingGroup(object part, string icon)
+		public static Drawing LoadDrawingGroup(object? part, string icon)
 		{
 			return (Drawing)Application.LoadComponent(GetUri(part, icon + ".xaml", absolute: false));
 		}
 
-		private static Uri GetUri(object part, string icon, bool absolute = true)
+		private static Uri GetUri(object? part, string icon, bool absolute = true)
 		{
 			Uri uri;
 			var assembly = part?.GetType().Assembly;
@@ -212,15 +212,15 @@ namespace ICSharpCode.ILSpy
 				return memberIconCache.GetIcon(icon, overlay, isStatic);
 		}
 
-		private static ImageSource GetIcon(string baseImage, string overlay = null, bool isStatic = false)
+		private static ImageSource GetIcon(string baseImage, string? overlay = null, bool isStatic = false)
 		{
 			ImageSource baseImageSource = Load(baseImage);
-			ImageSource overlayImageSource = overlay != null ? Load(overlay) : null;
+			ImageSource? overlayImageSource = overlay != null ? Load(overlay) : null;
 
 			return CreateOverlayImage(baseImageSource, overlayImageSource, isStatic);
 		}
 
-		private static ImageSource CreateOverlayImage(ImageSource baseImage, ImageSource overlay, bool isStatic)
+		private static ImageSource CreateOverlayImage(ImageSource baseImage, ImageSource? overlay, bool isStatic)
 		{
 			var group = new DrawingGroup();
 
@@ -391,16 +391,16 @@ namespace ICSharpCode.ILSpy
 			private ImageSource BuildMemberIcon(T icon, AccessOverlayIcon overlay, bool isStatic)
 			{
 				ImageSource baseImage = GetBaseImage(icon);
-				ImageSource overlayImage = GetOverlayImage(overlay);
+				ImageSource? overlayImage = GetOverlayImage(overlay);
 
 				return CreateOverlayImage(baseImage, overlayImage, isStatic);
 			}
 
 			protected abstract ImageSource GetBaseImage(T icon);
 
-			private static ImageSource GetOverlayImage(AccessOverlayIcon overlay)
+			private static ImageSource? GetOverlayImage(AccessOverlayIcon overlay)
 			{
-				ImageSource overlayImage;
+				ImageSource? overlayImage;
 				switch (overlay)
 				{
 					case AccessOverlayIcon.Public:

ILSpy/Languages/CSharpHighlightingTokenWriter.cs

@@ -122,7 +122,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void WriteKeyword(Role role, string keyword)
 		{
-			HighlightingColor color = null;
+			HighlightingColor? color = null;
 			switch (keyword)
 			{
 				case "namespace":
@@ -299,7 +299,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void WritePrimitiveType(string type)
 		{
-			HighlightingColor color = null;
+			HighlightingColor? color = null;
 			switch (type)
 			{
 				case "new":
@@ -348,7 +348,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void WriteIdentifier(Identifier identifier)
 		{
-			HighlightingColor color = null;
+			HighlightingColor? color = null;
 			if (identifier.Parent?.GetResolveResult() is ILVariableResolveResult rr)
 			{
 				if (rr.Variable.Kind == VariableKind.Parameter)
@@ -454,7 +454,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void WritePrimitiveValue(object value, Decompiler.CSharp.Syntax.LiteralFormat format)
 		{
-			HighlightingColor color = null;
+			HighlightingColor? color = null;
 			if (value is null)
 			{
 				color = valueKeywordColor;

ILSpy/Languages/CSharpLanguage.cs

@@ -95,7 +95,7 @@ namespace ICSharpCode.ILSpy
 			get { return ".csproj"; }
 		}
 
-		IReadOnlyList<LanguageVersion> versions;
+		IReadOnlyList<LanguageVersion>? versions;
 
 		public override IReadOnlyList<LanguageVersion> LanguageVersions {
 			get {
@@ -151,7 +151,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void DecompileMethod(IMethod method, ITextOutput output, DecompilationOptions options)
 		{
-			MetadataFile assembly = method.ParentModule.MetadataFile;
+			MetadataFile? assembly = method.ParentModule.MetadataFile;
 			CSharpDecompiler decompiler = CreateDecompiler(assembly, options);
 			AddReferenceAssemblyWarningMessage(assembly, output);
 			AddReferenceWarningMessage(assembly, output);
@@ -182,7 +182,7 @@ namespace ICSharpCode.ILSpy
 
 			public void Run(AstNode rootNode, TransformContext context)
 			{
-				ConstructorDeclaration ctorDecl = null;
+				ConstructorDeclaration? ctorDecl = null;
 				foreach (var node in rootNode.Children)
 				{
 					switch (node)
@@ -247,7 +247,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void DecompileProperty(IProperty property, ITextOutput output, DecompilationOptions options)
 		{
-			MetadataFile assembly = property.ParentModule.MetadataFile;
+			MetadataFile? assembly = property.ParentModule.MetadataFile;
 			CSharpDecompiler decompiler = CreateDecompiler(assembly, options);
 			AddReferenceAssemblyWarningMessage(assembly, output);
 			AddReferenceWarningMessage(assembly, output);
@@ -258,7 +258,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void DecompileField(IField field, ITextOutput output, DecompilationOptions options)
 		{
-			MetadataFile assembly = field.ParentModule.MetadataFile;
+			MetadataFile? assembly = field.ParentModule.MetadataFile;
 			CSharpDecompiler decompiler = CreateDecompiler(assembly, options);
 			AddReferenceAssemblyWarningMessage(assembly, output);
 			AddReferenceWarningMessage(assembly, output);
@@ -348,7 +348,7 @@ namespace ICSharpCode.ILSpy
 
 		public override void DecompileType(ITypeDefinition type, ITextOutput output, DecompilationOptions options)
 		{
-			MetadataFile assembly = type.ParentModule.MetadataFile;
+			MetadataFile? assembly = type.ParentModule.MetadataFile;
 			CSharpDecompiler decompiler = CreateDecompiler(assembly, options);
 			AddReferenceAssemblyWarningMessage(assembly, output);
 			AddReferenceWarningMessage(assembly, output);
@@ -380,8 +380,8 @@ namespace ICSharpCode.ILSpy
 			AddWarningMessage(module, output, line1);
 		}
 
-		void AddWarningMessage(MetadataFile module, ITextOutput output, string line1, string line2 = null,
-			string buttonText = null, System.Windows.Media.ImageSource buttonImage = null, RoutedEventHandler buttonClickHandler = null)
+		void AddWarningMessage(MetadataFile module, ITextOutput output, string line1, string? line2 = null,
+			string? buttonText = null, System.Windows.Media.ImageSource? buttonImage = null, RoutedEventHandler? buttonClickHandler = null)
 		{
 			if (output is ISmartTextOutput fancyOutput)
 			{
@@ -775,7 +775,7 @@ namespace ICSharpCode.ILSpy
 
 		public override bool ShowMember(IEntity member)
 		{
-			MetadataFile assembly = member.ParentModule.MetadataFile;
+			MetadataFile? assembly = member.ParentModule?.MetadataFile;
 			return showAllMembers || !CSharpDecompiler.MemberIsHidden(assembly, member.MetadataToken, SettingsService.Instance.DecompilerSettings);
 		}
 

ILSpy/Languages/ILLanguage.cs

@@ -73,7 +73,7 @@ namespace ICSharpCode.ILSpy
 		public override void DecompileMethod(IMethod method, ITextOutput output, DecompilationOptions options)
 		{
 			var dis = CreateDisassembler(output, options);
-			MetadataFile module = method.ParentModule.MetadataFile;
+			MetadataFile? module = method.ParentModule?.MetadataFile;
 			dis.AssemblyResolver = module.GetAssemblyResolver();
 			dis.DebugInfo = module.GetDebugInfoOrNull();
 			dis.DisassembleMethod(module, (MethodDefinitionHandle)method.MetadataToken);
@@ -82,7 +82,7 @@ namespace ICSharpCode.ILSpy
 		public override void DecompileField(IField field, ITextOutput output, DecompilationOptions options)
 		{
 			var dis = CreateDisassembler(output, options);
-			MetadataFile module = field.ParentModule.MetadataFile;
+			MetadataFile? module = field.ParentModule?.MetadataFile;
 			dis.AssemblyResolver = module.GetAssemblyResolver();
 			dis.DebugInfo = module.GetDebugInfoOrNull();
 			dis.DisassembleField(module, (FieldDefinitionHandle)field.MetadataToken);
@@ -91,7 +91,7 @@ namespace ICSharpCode.ILSpy
 		public override void DecompileProperty(IProperty property, ITextOutput output, DecompilationOptions options)
 		{
 			var dis = CreateDisassembler(output, options);
-			MetadataFile module = property.ParentModule.MetadataFile;
+			MetadataFile? module = property.ParentModule?.MetadataFile;
 			dis.AssemblyResolver = module.GetAssemblyResolver();
 			dis.DebugInfo = module.GetDebugInfoOrNull();
 			dis.DisassembleProperty(module, (PropertyDefinitionHandle)property.MetadataToken);
@@ -117,7 +117,7 @@ namespace ICSharpCode.ILSpy
 		public override void DecompileEvent(IEvent ev, ITextOutput output, DecompilationOptions options)
 		{
 			var dis = CreateDisassembler(output, options);
-			MetadataFile module = ev.ParentModule.MetadataFile;
+			MetadataFile? module = ev.ParentModule?.MetadataFile;
 			dis.AssemblyResolver = module.GetAssemblyResolver();
 			dis.DebugInfo = module.GetDebugInfoOrNull();
 			dis.DisassembleEvent(module, (EventDefinitionHandle)ev.MetadataToken);
@@ -148,7 +148,7 @@ namespace ICSharpCode.ILSpy
 		public override void DecompileType(ITypeDefinition type, ITextOutput output, DecompilationOptions options)
 		{
 			var dis = CreateDisassembler(output, options);
-			MetadataFile module = type.ParentModule.MetadataFile;
+			MetadataFile? module = type.ParentModule?.MetadataFile;
 			dis.AssemblyResolver = module.GetAssemblyResolver();
 			dis.DebugInfo = module.GetDebugInfoOrNull();
 			dis.DisassembleType(module, (TypeDefinitionHandle)type.MetadataToken);
@@ -157,7 +157,7 @@ namespace ICSharpCode.ILSpy
 		public override void DecompileNamespace(string nameSpace, IEnumerable<ITypeDefinition> types, ITextOutput output, DecompilationOptions options)
 		{
 			var dis = CreateDisassembler(output, options);
-			MetadataFile module = types.FirstOrDefault()?.ParentModule.MetadataFile;
+			MetadataFile? module = types.FirstOrDefault()?.ParentModule?.MetadataFile;
 			dis.AssemblyResolver = module.GetAssemblyResolver();
 			dis.DebugInfo = module.GetDebugInfoOrNull();
 			dis.DisassembleNamespace(nameSpace, module, types.Select(t => (TypeDefinitionHandle)t.MetadataToken));
@@ -199,7 +199,7 @@ namespace ICSharpCode.ILSpy
 		{
 			var output = new AvalonEditTextOutput() { IgnoreNewLineAndIndent = true };
 			var disasm = CreateDisassembler(output, MainWindow.Instance.CreateDecompilationOptions());
-			MetadataFile module = entity.ParentModule?.MetadataFile;
+			MetadataFile? module = entity.ParentModule?.MetadataFile;
 			if (module == null)
 			{
 				return null;

ILSpy/Languages/Language.cs

@@ -125,7 +125,7 @@ namespace ICSharpCode.ILSpy
 				{
 					WriteCommentLine(output, metadata.GetString(name.Name) + " [WinRT]");
 				}
-				else if (metadata.TryGetFullAssemblyName(out string assemblyName))
+				else if (metadata.TryGetFullAssemblyName(out string? assemblyName))
 				{
 					WriteCommentLine(output, assemblyName);
 				}

ILSpy/MainWindow.xaml.cs

@@ -318,7 +318,7 @@ namespace ICSharpCode.ILSpy
 			{
 				return null;
 			}
-			string value = Properties.Resources.ResourceManager.GetString(key);
+			string? value = Properties.Resources.ResourceManager.GetString(key);
 			if (!string.IsNullOrEmpty(value))
 			{
 				return value;
@@ -659,13 +659,13 @@ namespace ICSharpCode.ILSpy
 					string namespaceName = navigateTo.Substring(2);
 					foreach (LoadedAssembly asm in relevantAssemblies)
 					{
-						AssemblyTreeNode asmNode = assemblyListTreeNode.FindAssemblyNode(asm);
+						AssemblyTreeNode? asmNode = assemblyListTreeNode.FindAssemblyNode(asm);
 						if (asmNode != null)
 						{
 							// FindNamespaceNode() blocks the UI if the assembly is not yet loaded,
 							// so use an async wait instead.
 							await asm.GetMetadataFileAsync().Catch<Exception>(ex => { });
-							NamespaceTreeNode nsNode = asmNode.FindNamespaceNode(namespaceName);
+							NamespaceTreeNode? nsNode = asmNode.FindNamespaceNode(namespaceName);
 							if (nsNode != null)
 							{
 								found = true;
@@ -686,7 +686,7 @@ namespace ICSharpCode.ILSpy
 				}
 				else
 				{
-					IEntity mr = await Task.Run(() => FindEntityInRelevantAssemblies(navigateTo, relevantAssemblies));
+					IEntity? mr = await Task.Run(() => FindEntityInRelevantAssemblies(navigateTo, relevantAssemblies));
 					// Make sure we wait for assemblies being loaded...
 					// BeginInvoke in LoadedAssembly.LookupReferencedAssemblyInternal
 					await Dispatcher.InvokeAsync(delegate { }, DispatcherPriority.Normal);
@@ -710,7 +710,7 @@ namespace ICSharpCode.ILSpy
 			{
 				// NavigateTo == null and an assembly was given on the command-line:
 				// Select the newly loaded assembly
-				AssemblyTreeNode asmNode = assemblyListTreeNode.FindAssemblyNode(relevantAssemblies[0]);
+				AssemblyTreeNode? asmNode = assemblyListTreeNode.FindAssemblyNode(relevantAssemblies[0]);
 				if (asmNode != null && AssemblyTreeView.SelectedItem == initialSelection)
 				{
 					SelectNode(asmNode);
@@ -718,7 +718,7 @@ namespace ICSharpCode.ILSpy
 			}
 			else if (spySettings != null)
 			{
-				SharpTreeNode node = null;
+				SharpTreeNode? node = null;
 				if (activeTreeViewPath?.Length > 0)
 				{
 					foreach (var asm in CurrentAssemblyList.GetAssemblies())
@@ -772,7 +772,7 @@ namespace ICSharpCode.ILSpy
 						: new SimpleCompilation((PEFile)module, MinimalCorlib.Instance);
 					return memberRef == null
 						? typeRef.Resolve(new SimpleTypeResolveContext(compilation)) as ITypeDefinition
-						: (IEntity)memberRef.Resolve(new SimpleTypeResolveContext(compilation));
+						: (IEntity?)memberRef.Resolve(new SimpleTypeResolveContext(compilation));
 				}
 			}
 			return null;
@@ -875,7 +875,7 @@ namespace ICSharpCode.ILSpy
 
 		public async Task ShowMessageIfUpdatesAvailableAsync(ILSpySettings spySettings, bool forceCheck = false)
 		{
-			string downloadUrl;
+			string? downloadUrl;
 			if (forceCheck)
 			{
 				downloadUrl = await NotifyOfUpdatesStrategy.CheckForUpdatesAsync(spySettings);
@@ -903,12 +903,12 @@ namespace ICSharpCode.ILSpy
 			else
 			{
 				updatePanel.Visibility = Visibility.Collapsed;
-				string downloadUrl = await NotifyOfUpdatesStrategy.CheckForUpdatesAsync(ILSpySettings.Load());
+				string? downloadUrl = await NotifyOfUpdatesStrategy.CheckForUpdatesAsync(ILSpySettings.Load());
 				AdjustUpdateUIAfterCheck(downloadUrl, true);
 			}
 		}
 
-		void AdjustUpdateUIAfterCheck(string downloadUrl, bool displayMessage)
+		void AdjustUpdateUIAfterCheck(string? downloadUrl, bool displayMessage)
 		{
 			updateAvailableDownloadUrl = downloadUrl;
 			updatePanel.Visibility = displayMessage ? Visibility.Visible : Visibility.Collapsed;
@@ -1113,8 +1113,8 @@ namespace ICSharpCode.ILSpy
 		{
 			if (path == null)
 				return null;
-			SharpTreeNode node = AssemblyTreeView.Root;
-			SharpTreeNode bestMatch = node;
+			SharpTreeNode? node = AssemblyTreeView.Root;
+			SharpTreeNode? bestMatch = node;
 			foreach (var element in path)
 			{
 				if (node == null)
@@ -1237,7 +1237,7 @@ namespace ICSharpCode.ILSpy
 					}
 					break;
 				default:
-					ILSpyTreeNode treeNode = FindTreeNode(reference);
+					ILSpyTreeNode? treeNode = FindTreeNode(reference);
 					if (treeNode != null)
 						SelectNode(treeNode, inNewTabPage);
 					break;
@@ -1301,9 +1301,9 @@ namespace ICSharpCode.ILSpy
 			LoadAssemblies(fileNames, focusNode: focusNode);
 		}
 
-		void LoadAssemblies(IEnumerable<string> fileNames, List<LoadedAssembly> loadedAssemblies = null, bool focusNode = true)
+		void LoadAssemblies(IEnumerable<string> fileNames, List<LoadedAssembly>? loadedAssemblies = null, bool focusNode = true)
 		{
-			SharpTreeNode lastNode = null;
+			SharpTreeNode? lastNode = null;
 			foreach (string file in fileNames)
 			{
 				var asm = assemblyList.OpenAssembly(file);
@@ -1367,7 +1367,7 @@ namespace ICSharpCode.ILSpy
 
 		void TreeView_SelectionChanged(object sender, SelectionChangedEventArgs e)
 		{
-			DecompilerTextViewState state = null;
+			DecompilerTextViewState? state = null;
 			if (refreshInProgress || changingActiveTab)
 			{
 				state = DockWorkspace.Instance.ActiveTabPage.GetState() as DecompilerTextViewState;
@@ -1385,7 +1385,7 @@ namespace ICSharpCode.ILSpy
 		Task decompilationTask;
 		bool ignoreDecompilationRequests;
 
-		void DecompileSelectedNodes(DecompilerTextViewState newState = null, bool recordHistory = true)
+		void DecompileSelectedNodes(DecompilerTextViewState? newState = null, bool recordHistory = true)
 		{
 			if (ignoreDecompilationRequests)
 				return;
@@ -1406,7 +1406,7 @@ namespace ICSharpCode.ILSpy
 
 			if (AssemblyTreeView.SelectedItems.Count == 1)
 			{
-				ILSpyTreeNode node = AssemblyTreeView.SelectedItem as ILSpyTreeNode;
+				ILSpyTreeNode? node = AssemblyTreeView.SelectedItem as ILSpyTreeNode;
 				if (node != null && node.View(DockWorkspace.Instance.ActiveTabPage))
 					return;
 			}
@@ -1533,11 +1533,11 @@ namespace ICSharpCode.ILSpy
 					Title = e.Uri.AbsolutePath,
 					EnableHyperlinks = true
 				};
-				using (Stream s = typeof(App).Assembly.GetManifestResourceStream(typeof(App), e.Uri.AbsolutePath))
+				using (Stream? s = typeof(App).Assembly.GetManifestResourceStream(typeof(App), e.Uri.AbsolutePath))
 				{
 					using (StreamReader r = new StreamReader(s))
 					{
-						string line;
+						string? line;
 						while ((line = r.ReadLine()) != null)
 						{
 							output.Write(line);

ILSpy/Metadata/CorTables/EventTableTreeNode.cs

@@ -92,7 +92,7 @@ namespace ICSharpCode.ILSpy.Metadata
 
 			public string Name => metadataFile.Metadata.GetString(eventDef.Name);
 
-			IEntity IMemberTreeNode.Member {
+			IEntity? IMemberTreeNode.Member {
 				get {
 					return ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule)?.GetDefinition(handle);
 				}

ILSpy/Metadata/CorTables/FieldTableTreeNode.cs

@@ -95,7 +95,7 @@ namespace ICSharpCode.ILSpy.Metadata
 
 			public string NameTooltip => $"{MetadataTokens.GetHeapOffset(fieldDef.Name):X} \"{Name}\"";
 
-			IEntity IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule)?.GetDefinition(handle);
+			IEntity? IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule)?.GetDefinition(handle);
 
 			[ColumnInfo("X8", Kind = ColumnKind.HeapOffset)]
 			public int Signature => MetadataTokens.GetHeapOffset(fieldDef.Signature);

ILSpy/Metadata/CorTables/MethodTableTreeNode.cs

@@ -131,7 +131,7 @@ namespace ICSharpCode.ILSpy.Metadata
 				}
 			}
 
-			IEntity IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule)?.GetDefinition(handle);
+			IEntity? IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule)?.GetDefinition(handle);
 
 			public MethodDefEntry(MetadataFile metadataFile, MethodDefinitionHandle handle)
 			{

ILSpy/Metadata/CorTables/PropertyTableTreeNode.cs

@@ -92,7 +92,7 @@ namespace ICSharpCode.ILSpy.Metadata
 
 			public string NameTooltip => $"{MetadataTokens.GetHeapOffset(propertyDef.Name):X} \"{Name}\"";
 
-			IEntity IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule).GetDefinition(handle);
+			IEntity? IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule).GetDefinition(handle);
 
 			[ColumnInfo("X8", Kind = ColumnKind.HeapOffset)]
 			public int Signature => MetadataTokens.GetHeapOffset(propertyDef.Signature);

ILSpy/Metadata/CorTables/TypeDefTableTreeNode.cs

@@ -173,7 +173,7 @@ namespace ICSharpCode.ILSpy.Metadata
 				}
 			}
 
-			IEntity IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule).GetDefinition(handle);
+			IEntity? IMemberTreeNode.Member => ((MetadataModule)metadataFile.GetTypeSystemWithCurrentOptionsOrNull()?.MainModule).GetDefinition(handle);
 
 			public TypeDefEntry(MetadataFile metadataFile, TypeDefinitionHandle handle)
 			{

ILSpy/Metadata/DebugTables/CustomDebugInformationTableTreeNode.cs

@@ -47,7 +47,7 @@ namespace ICSharpCode.ILSpy.Metadata
 			view.RowDetailsTemplateSelector = new CustomDebugInformationDetailsTemplateSelector();
 
 			var list = new List<CustomDebugInformationEntry>();
-			CustomDebugInformationEntry scrollTargetEntry = default;
+			CustomDebugInformationEntry? scrollTargetEntry = default;
 
 			foreach (var row in metadataFile.Metadata.CustomDebugInformation)
 			{

ILSpy/Metadata/GoToTokenCommand.cs

@@ -51,7 +51,7 @@ namespace ICSharpCode.ILSpy.Commands
 			return context.DataGrid?.Name == "MetadataView" && GetSelectedToken(context.DataGrid, out _) != null;
 		}
 
-		private int? GetSelectedToken(DataGrid grid, out MetadataFile module)
+		private int? GetSelectedToken(DataGrid grid, out MetadataFile? module)
 		{
 			module = null;
 			if (grid == null)
@@ -75,7 +75,7 @@ namespace ICSharpCode.ILSpy.Commands
 	{
 		public void Execute(TextViewContext context)
 		{
-			string content = GetSelectedCellContent(context.DataGrid, context.MousePosition);
+			string? content = GetSelectedCellContent(context.DataGrid, context.MousePosition);
 			Clipboard.SetText(content);
 		}
 

ILSpy/NavigationState.cs

@@ -38,7 +38,7 @@ namespace ICSharpCode.ILSpy
 		public NavigationState(TabPageModel tabPage, ViewState viewState)
 		{
 			this.TabPage = tabPage;
-			this.treeNodes = new HashSet<SharpTreeNode>((IEnumerable<SharpTreeNode>)viewState.DecompiledNodes ?? Array.Empty<SharpTreeNode>());
+			this.treeNodes = new HashSet<SharpTreeNode>((IEnumerable<SharpTreeNode>?)viewState.DecompiledNodes ?? Array.Empty<SharpTreeNode>());
 			ViewState = viewState;
 		}
 

ILSpy/Options/DisplaySettingsPanel.xaml.cs

@@ -99,11 +99,11 @@ namespace ICSharpCode.ILSpy.Options
 					select ff).ToArray();
 		}
 
-		public static DisplaySettings LoadDisplaySettings(ILSpySettings settings, SessionSettings sessionSettings = null)
+		public static DisplaySettings LoadDisplaySettings(ILSpySettings settings, SessionSettings? sessionSettings = null)
 		{
 			XElement e = settings["DisplaySettings"];
 			var s = new DisplaySettings();
-			s.SelectedFont = new FontFamily((string)e.Attribute("Font") ?? "Consolas");
+			s.SelectedFont = new FontFamily((string?)e.Attribute("Font") ?? "Consolas");
 			s.SelectedFontSize = (double?)e.Attribute("FontSize") ?? 10.0 * 4 / 3;
 			s.ShowLineNumbers = (bool?)e.Attribute("ShowLineNumbers") ?? false;
 			s.ShowMetadataTokens = (bool?)e.Attribute("ShowMetadataTokens") ?? false;

ILSpy/Options/OptionsDialog.xaml.cs

@@ -63,7 +63,7 @@ namespace ICSharpCode.ILSpy.Options
 
 				tabControl.Items.Add(tabItem);
 
-				IOptionPage page = optionPage.Value as IOptionPage;
+				IOptionPage? page = optionPage.Value as IOptionPage;
 				if (page != null)
 					page.Load(settings);
 			}
@@ -75,7 +75,7 @@ namespace ICSharpCode.ILSpy.Options
 				delegate (XElement root) {
 					foreach (var optionPage in optionPages)
 					{
-						IOptionPage page = optionPage.Value as IOptionPage;
+						IOptionPage? page = optionPage.Value as IOptionPage;
 						if (page != null)
 							page.Save(root);
 					}

ILSpy/Search/SearchPane.xaml.cs

@@ -53,7 +53,7 @@ namespace ICSharpCode.ILSpy.Search
 	{
 		const int MAX_RESULTS = 1000;
 		const int MAX_REFRESH_TIME_MS = 10; // More means quicker forward of data, fewer means better responsibility
-		RunningSearch currentSearch;
+		RunningSearch? currentSearch;
 		bool runSearchOnNextShow;
 		IComparer<SearchResult> resultsComparer;
 
@@ -231,7 +231,7 @@ namespace ICSharpCode.ILSpy.Search
 			currentSearch.Cancel();
 		}
 
-		async void StartSearch(string searchTerm)
+		async void StartSearch(string? searchTerm)
 		{
 			if (currentSearch != null)
 			{
@@ -245,7 +245,7 @@ namespace ICSharpCode.ILSpy.Search
 				SearchResult.ComparerByName;
 			Results.Clear();
 
-			RunningSearch startedSearch = null;
+			RunningSearch? startedSearch = null;
 			if (!string.IsNullOrEmpty(searchTerm))
 			{
 
@@ -299,7 +299,7 @@ namespace ICSharpCode.ILSpy.Search
 
 				SearchRequest request = new();
 				List<string> keywords = new();
-				Regex regex = null;
+				Regex? regex = null;
 				request.Mode = searchMode;
 
 				foreach (string part in parts)
@@ -325,7 +325,7 @@ namespace ICSharpCode.ILSpy.Search
 						prefixLength = part.IndexOf(':', 0, prefixLength);
 						delimiterLength = 1;
 					}
-					string prefix;
+					string? prefix;
 					if (prefixLength <= 0)
 					{
 						prefix = null;

ILSpy/SessionSettings.cs

@@ -44,7 +44,7 @@ namespace ICSharpCode.ILSpy
 		{
 			XElement doc = spySettings["SessionSettings"];
 
-			XElement filterSettings = doc.Element("FilterSettings");
+			XElement? filterSettings = doc.Element("FilterSettings");
 			if (filterSettings == null)
 				filterSettings = new XElement("FilterSettings");
 
@@ -52,7 +52,7 @@ namespace ICSharpCode.ILSpy
 
 			this.ActiveAssemblyList = (string)doc.Element("ActiveAssemblyList");
 
-			XElement activeTreeViewPath = doc.Element("ActiveTreeViewPath");
+			XElement? activeTreeViewPath = doc.Element("ActiveTreeViewPath");
 			if (activeTreeViewPath != null)
 			{
 				this.ActiveTreeViewPath = activeTreeViewPath.Elements().Select(e => Unescape((string)e)).ToArray();
@@ -63,7 +63,7 @@ namespace ICSharpCode.ILSpy
 			this.WindowBounds = FromString((string)doc.Element("WindowBounds"), DefaultWindowBounds);
 			this.SelectedSearchMode = FromString((string)doc.Element("SelectedSearchMode"), SearchMode.TypeAndMember);
 			this.Theme = FromString((string)doc.Element(nameof(Theme)), ThemeManager.Current.DefaultTheme);
-			string currentCulture = (string)doc.Element(nameof(CurrentCulture));
+			string? currentCulture = (string)doc.Element(nameof(CurrentCulture));
 			this.CurrentCulture = string.IsNullOrEmpty(currentCulture) ? null : currentCulture;
 
 			this.DockLayout = new DockLayoutSettings(doc.Element("DockLayout"));
@@ -108,7 +108,7 @@ namespace ICSharpCode.ILSpy
 			}
 		}
 
-		public string ActiveAssemblyList {
+		public string? ActiveAssemblyList {
 			get => activeAssemblyList;
 			set {
 				if (value != null && value != activeAssemblyList)
@@ -166,7 +166,7 @@ namespace ICSharpCode.ILSpy
 		}
 
 		static Regex regex = new Regex("\\\\x(?<num>[0-9A-f]{4})");
-		private string activeAssemblyList;
+		private string? activeAssemblyList;
 
 		static string Escape(string p)
 		{
@@ -186,7 +186,7 @@ namespace ICSharpCode.ILSpy
 			return regex.Replace(p, m => ((char)int.Parse(m.Groups["num"].Value, NumberStyles.HexNumber)).ToString());
 		}
 
-		static T FromString<T>(string s, T defaultValue)
+		static T FromString<T>(string? s, T defaultValue)
 		{
 			if (s == null)
 				return defaultValue;

ILSpy/TaskHelper.cs

@@ -174,7 +174,7 @@ namespace ICSharpCode.ILSpy
 			return task.ContinueWith(t => {
 				if (t.IsFaulted)
 				{
-					Exception ex = t.Exception;
+					Exception? ex = t.Exception;
 					while (ex is AggregateException)
 						ex = ex.InnerException;
 					if (ex is TException)

ILSpy/TextView/AvalonEditTextOutput.cs

@@ -40,7 +40,7 @@ namespace ICSharpCode.ILSpy.TextView
 	/// </summary>
 	public sealed class ReferenceSegment : TextSegment
 	{
-		public object Reference;
+		public object? Reference;
 		public bool IsLocal;
 		public bool IsDefinition;
 	}

ILSpy/TextView/DecompilerTextView.cs

@@ -392,7 +392,7 @@ namespace ICSharpCode.ILSpy.TextView
 		{
 			if (segment.Reference is ICSharpCode.Decompiler.Disassembler.OpCodeInfo code)
 			{
-				XmlDocumentationProvider docProvider = XmlDocLoader.MscorlibDocumentation;
+				XmlDocumentationProvider? docProvider = XmlDocLoader.MscorlibDocumentation;
 				DocumentationUIBuilder renderer = new DocumentationUIBuilder(new CSharpAmbience(), SettingsService.Instance.SessionSettings.LanguageSettings.Language.SyntaxHighlighting);
 				renderer.AddSignatureBlock($"{code.Name} (0x{code.Code:x})");
 				if (docProvider != null)
@@ -425,7 +425,7 @@ namespace ICSharpCode.ILSpy.TextView
 					Handle handle = unresolvedEntity.Handle;
 					if (!handle.IsEntityHandle())
 						return null;
-					IEntity resolved = typeSystem.MainModule.ResolveEntity((EntityHandle)handle);
+					IEntity? resolved = typeSystem.MainModule.ResolveEntity((EntityHandle)handle);
 					if (resolved == null)
 						return null;
 					var document = CreateTooltipForEntity(resolved);
@@ -445,7 +445,7 @@ namespace ICSharpCode.ILSpy.TextView
 		{
 			Language currentLanguage = SettingsService.Instance.SessionSettings.LanguageSettings.Language;
 			DocumentationUIBuilder renderer = new DocumentationUIBuilder(new CSharpAmbience(), currentLanguage.SyntaxHighlighting);
-			RichText richText = currentLanguage.GetRichTextTooltip(resolved);
+			RichText? richText = currentLanguage.GetRichTextTooltip(resolved);
 			if (richText == null)
 			{
 				return null;

ILSpy/TextView/DocumentationUIBuilder.cs

@@ -128,7 +128,7 @@ namespace ICSharpCode.ILSpy.TextView
 			AddBlock(block);
 		}
 
-		public void AddXmlDocumentation(string xmlDocumentation, IEntity declaringEntity, Func<string, IEntity?> resolver)
+		public void AddXmlDocumentation(string xmlDocumentation, IEntity? declaringEntity, Func<string, IEntity?>? resolver)
 		{
 			if (xmlDocumentation == null)
 				return;
@@ -375,7 +375,7 @@ namespace ICSharpCode.ILSpy.TextView
 
 		void AddSee(XmlDocumentationElement element)
 		{
-			IEntity referencedEntity = element.ReferencedEntity;
+			IEntity? referencedEntity = element.ReferencedEntity;
 			if (referencedEntity != null)
 			{
 				if (element.Children.Any())
@@ -397,7 +397,7 @@ namespace ICSharpCode.ILSpy.TextView
 			}
 			else if (element.GetAttribute("href") != null)
 			{
-				Uri uri;
+				Uri? uri;
 				if (Uri.TryCreate(element.GetAttribute("href"), UriKind.Absolute, out uri))
 				{
 					if (element.Children.Any())

ILSpy/TextView/FoldingCommands.cs

@@ -43,7 +43,7 @@ namespace ICSharpCode.ILSpy.TextView
 		{
 			if (null == context.TextView)
 				return;
-			FoldingManager foldingManager = context.TextView.FoldingManager;
+			FoldingManager? foldingManager = context.TextView.FoldingManager;
 			if (null == foldingManager)
 				return;
 			bool doFold = true;
@@ -82,7 +82,7 @@ namespace ICSharpCode.ILSpy.TextView
 			if (null == textView)
 				return;
 			var editor = textView.textEditor;
-			FoldingManager foldingManager = context.TextView.FoldingManager;
+			FoldingManager? foldingManager = context.TextView.FoldingManager;
 			if (null == foldingManager)
 				return;
 			// TODO: or use Caret if position is not given?
@@ -91,7 +91,7 @@ namespace ICSharpCode.ILSpy.TextView
 				return;
 			TextViewPosition pos = posBox.Value;
 			// look for folding on this line:
-			FoldingSection folding = foldingManager.GetNextFolding(editor.Document.GetOffset(pos.Line, 1));
+			FoldingSection? folding = foldingManager.GetNextFolding(editor.Document.GetOffset(pos.Line, 1));
 			if (folding == null || editor.Document.GetLineByOffset(folding.StartOffset).LineNumber != pos.Line)
 			{
 				// no folding found on current line: find innermost folding containing the mouse position

ILSpy/TreeNodes/AssemblyListTreeNode.cs

@@ -98,7 +98,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		public override void Drop(IPlatformDragEventArgs e, int index)
 		{
-			string[] files = e.Data.GetData(AssemblyTreeNode.DataFormat) as string[];
+			string[]? files = e.Data.GetData(AssemblyTreeNode.DataFormat) as string[];
 			if (files == null)
 				files = e.Data.GetData(DataFormats.FileDrop) as string[];
 			if (files != null)
@@ -225,7 +225,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			var declaringType = def.DeclaringTypeDefinition;
 			if (declaringType != null)
 			{
-				TypeTreeNode decl = FindTypeNode(declaringType);
+				TypeTreeNode? decl = FindTypeNode(declaringType);
 				if (decl != null)
 				{
 					decl.EnsureLazyChildren();
@@ -249,12 +249,12 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		/// </summary>
 		public ILSpyTreeNode? FindMethodNode(IMethod def)
 		{
-			TypeTreeNode typeNode = FindTypeNode(def.DeclaringTypeDefinition);
+			TypeTreeNode? typeNode = FindTypeNode(def.DeclaringTypeDefinition);
 			if (typeNode == null)
 				return null;
 			// method might be an accessor, must look for parent node
-			ILSpyTreeNode parentNode = typeNode;
-			MethodTreeNode methodNode;
+			ILSpyTreeNode? parentNode = typeNode;
+			MethodTreeNode? methodNode;
 			parentNode.EnsureLazyChildren();
 			switch (def.AccessorOwner)
 			{
@@ -290,7 +290,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		/// </summary>
 		public FieldTreeNode? FindFieldNode(IField def)
 		{
-			TypeTreeNode typeNode = FindTypeNode(def.DeclaringTypeDefinition);
+			TypeTreeNode? typeNode = FindTypeNode(def.DeclaringTypeDefinition);
 			if (typeNode == null)
 				return null;
 			typeNode.EnsureLazyChildren();
@@ -303,7 +303,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		/// </summary>
 		public PropertyTreeNode? FindPropertyNode(IProperty def)
 		{
-			TypeTreeNode typeNode = FindTypeNode(def.DeclaringTypeDefinition);
+			TypeTreeNode? typeNode = FindTypeNode(def.DeclaringTypeDefinition);
 			if (typeNode == null)
 				return null;
 			typeNode.EnsureLazyChildren();
@@ -316,7 +316,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		/// </summary>
 		public EventTreeNode? FindEventNode(IEvent def)
 		{
-			TypeTreeNode typeNode = FindTypeNode(def.DeclaringTypeDefinition);
+			TypeTreeNode? typeNode = FindTypeNode(def.DeclaringTypeDefinition);
 			if (typeNode == null)
 				return null;
 			typeNode.EnsureLazyChildren();

ILSpy/TreeNodes/AssemblyTreeNode.cs

@@ -248,7 +248,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			typeSystem = LoadedAssembly.GetTypeSystemOrNull();
 			var assembly = (MetadataModule)typeSystem.MainModule;
 			this.Children.Add(new MetadataTreeNode(module, Resources.Metadata));
-			Decompiler.DebugInfo.IDebugInfoProvider debugInfo = LoadedAssembly.GetDebugInfoOrNull();
+			Decompiler.DebugInfo.IDebugInfoProvider? debugInfo = LoadedAssembly.GetDebugInfoOrNull();
 			if (debugInfo is PortableDebugInfoProvider ppdb
 				&& ppdb.GetMetadataReader() is System.Reflection.Metadata.MetadataReader reader)
 			{
@@ -280,7 +280,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 			NamespaceTreeNode GetOrCreateNamespaceTreeNode(string @namespace)
 			{
-				if (!namespaces.TryGetValue(@namespace, out NamespaceTreeNode ns))
+				if (!namespaces.TryGetValue(@namespace, out NamespaceTreeNode? ns))
 				{
 					if (useNestedStructure)
 					{
@@ -346,7 +346,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 			NamespaceTreeNode GetOrCreateNamespaceTreeNode(string @namespace)
 			{
-				if (!namespaces.TryGetValue(@namespace, out NamespaceTreeNode ns))
+				if (!namespaces.TryGetValue(@namespace, out NamespaceTreeNode? ns))
 				{
 					if (useNestedStructure)
 					{
@@ -392,7 +392,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			if (type == null)
 				return null;
 			EnsureLazyChildren();
-			TypeTreeNode node;
+			TypeTreeNode? node;
 			if (typeDict.TryGetValue((TypeDefinitionHandle)type.MetadataToken, out node))
 				return node;
 			else

ILSpy/TreeNodes/ResourceNodes/ResourceTreeNode.cs

@@ -71,7 +71,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			var sizeInBytesText = sizeInBytes == null ? "" : ", " + sizeInBytes + " bytes";
 			language.WriteCommentLine(output, $"{Resource.Name} ({Resource.ResourceType}, {Resource.Attributes}{sizeInBytesText})");
 
-			ISmartTextOutput smartOutput = output as ISmartTextOutput;
+			ISmartTextOutput? smartOutput = output as ISmartTextOutput;
 			if (smartOutput != null)
 			{
 				smartOutput.AddButton(Images.Save, Resources.Save, delegate { Save(Docking.DockWorkspace.Instance.ActiveTabPage); });
@@ -81,7 +81,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		public override bool View(TabPageModel tabPage)
 		{
-			Stream s = Resource.TryOpenStream();
+			Stream? s = Resource.TryOpenStream();
 			if (s != null && s.Length < DecompilerTextView.DefaultOutputLengthLimit)
 			{
 				s.Position = 0;
@@ -107,7 +107,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		public override bool Save(TabPageModel tabPage)
 		{
-			Stream s = Resource.TryOpenStream();
+			Stream? s = Resource.TryOpenStream();
 			if (s == null)
 				return false;
 			SaveFileDialog dlg = new SaveFileDialog();

ILSpy/TreeNodes/ResourceNodes/ResourcesFileTreeNode.cs

@@ -71,7 +71,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		protected override void LoadChildren()
 		{
-			Stream s = Resource.TryOpenStream();
+			Stream? s = Resource.TryOpenStream();
 			if (s == null)
 				return;
 			s.Position = 0;
@@ -128,7 +128,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		public override bool Save(TabPageModel tabPage)
 		{
-			Stream s = Resource.TryOpenStream();
+			Stream? s = Resource.TryOpenStream();
 			if (s == null)
 				return false;
 			SaveFileDialog dlg = new SaveFileDialog();
@@ -179,7 +179,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			var textView = (DecompilerTextView)Docking.DockWorkspace.Instance.ActiveTabPage.Content;
 			if (stringTableEntries.Count != 0)
 			{
-				ISmartTextOutput smartOutput = output as ISmartTextOutput;
+				ISmartTextOutput? smartOutput = output as ISmartTextOutput;
 				if (null != smartOutput)
 				{
 					smartOutput.AddUIElement(
@@ -193,7 +193,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			}
 			if (otherEntries.Count != 0)
 			{
-				ISmartTextOutput smartOutput = output as ISmartTextOutput;
+				ISmartTextOutput? smartOutput = output as ISmartTextOutput;
 				if (null != smartOutput)
 				{
 					smartOutput.AddUIElement(

ILSpy/TreeNodes/ResourceNodes/XamlResourceNode.cs

@@ -54,7 +54,7 @@ namespace ICSharpCode.ILSpy.Xaml
 		public override bool View(TabPageModel tabPage)
 		{
 			AvalonEditTextOutput output = new AvalonEditTextOutput();
-			IHighlightingDefinition highlighting = null;
+			IHighlightingDefinition? highlighting = null;
 
 			tabPage.ShowTextView(textView => textView.RunWithCancellation(
 				token => Task.Factory.StartNew(

ILSpy/TreeNodes/ThreadingSupport.cs

@@ -67,7 +67,7 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			CancellationToken ct = cancellationTokenSource.Token;
 
 			var fetchChildrenEnumerable = fetchChildren(ct);
-			Task<List<SharpTreeNode>> thisTask = null;
+			Task<List<SharpTreeNode>>? thisTask = null;
 			thisTask = new Task<List<SharpTreeNode>>(
 				delegate {
 					List<SharpTreeNode> result = new List<SharpTreeNode>();

ILSpy/Updates/NotifyOfUpdatesStrategy.cs

@@ -46,7 +46,7 @@ namespace ICSharpCode.ILSpy.Updates
 			var bands = doc.Root.Elements("band");
 			var currentBand = bands.FirstOrDefault(b => (string)b.Attribute("id") == band) ?? bands.First();
 			Version version = new Version((string)currentBand.Element("latestVersion"));
-			string url = (string)currentBand.Element("downloadUrl");
+			string? url = (string)currentBand.Element("downloadUrl");
 			if (!(url.StartsWith("http://", StringComparison.Ordinal) || url.StartsWith("https://", StringComparison.Ordinal)))
 				url = null; // don't accept non-urls
 

TestPlugin/CustomLanguage.cs

@@ -41,7 +41,7 @@ namespace TestPlugin
 				var methodBody = module.GetMethodBody(methodDef.RelativeVirtualAddress);
 				output.WriteLine("Size of method: {0} bytes", methodBody.GetCodeSize());
 
-				ISmartTextOutput smartOutput = output as ISmartTextOutput;
+				ISmartTextOutput? smartOutput = output as ISmartTextOutput;
 				if (smartOutput != null)
 				{
 					// when writing to the text view (but not when writing to a file), we can even add UI elements such as buttons:

TestPlugin/CustomOptionPage.xaml.cs

@@ -50,7 +50,7 @@ namespace TestPlugin
 
 			// Replace the existing section in the settings file, or add a new section,
 			// if required.
-			XElement existingElement = root.Element(ns + "CustomOptions");
+			XElement? existingElement = root.Element(ns + "CustomOptions");
 			if (existingElement != null)
 				existingElement.ReplaceWith(section);
 			else