diff --git a/src/EditorFeatures/CSharp/BlockCommentEditing/BlockCommentEditingCommandHandler.cs b/src/EditorFeatures/CSharp/BlockCommentEditing/BlockCommentEditingCommandHandler.cs
index f69be48b621220367b5c62d08e8f6ea0952ec0a5..c6d12c1248cf122a4e3da4b6b941602a19394543 100644
--- a/src/EditorFeatures/CSharp/BlockCommentEditing/BlockCommentEditingCommandHandler.cs
+++ b/src/EditorFeatures/CSharp/BlockCommentEditing/BlockCommentEditingCommandHandler.cs
@@ -2,9 +2,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using System.ComponentModel.Composition;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Editor.Shared.Extensions;
@@ -88,7 +91,7 @@ private Span GetReplacementSpan(SnapshotPoint caretPosition)
             return Span.FromBounds(start, end);
         }
 
-        private string GetTextToInsert(SnapshotPoint caretPosition)
+        private string? GetTextToInsert(SnapshotPoint caretPosition)
         {
             var currentLine = caretPosition.GetContainingLine();
             var firstNonWhitespacePosition = currentLine.GetFirstNonWhitespacePosition() ?? -1;
@@ -128,7 +131,7 @@ private string GetTextToInsert(SnapshotPoint caretPosition)
             var newLine = options.GetOption(FormattingOptions.NewLine, LanguageNames.CSharp);
             return newLine + exteriorText;
 
-            string GetExteriorText()
+            string? GetExteriorText()
             {
                 if (startsWithBlockCommentStartString)
                 {
@@ -231,7 +234,8 @@ private static bool BlockCommentEndsRightAfterCaret(SnapshotPoint caretPosition)
         }
 
         public static bool IsCaretInsideBlockCommentSyntax(
-            SnapshotPoint caretPosition, out Document document, out SyntaxTrivia trivia)
+            SnapshotPoint caretPosition,
+            [NotNullWhen(true)] out Document? document, out SyntaxTrivia trivia)
         {
             trivia = default;
 
@@ -240,7 +244,7 @@ private static bool BlockCommentEndsRightAfterCaret(SnapshotPoint caretPosition)
             if (document == null)
                 return false;
 
-            var syntaxTree = document.GetSyntaxTreeSynchronously(CancellationToken.None);
+            var syntaxTree = document.GetRequiredSyntaxTreeSynchronously(CancellationToken.None);
             trivia = syntaxTree.FindTriviaAndAdjustForEndOfFile(caretPosition, CancellationToken.None);
 
             var isBlockComment = trivia.IsKind(SyntaxKind.MultiLineCommentTrivia) || trivia.IsKind(SyntaxKind.MultiLineDocumentationCommentTrivia);
diff --git a/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Extensions/DocumentExtensions.cs b/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Extensions/DocumentExtensions.cs
index 9c189e5a3f15c42e0f8df1799ed77f4dac7d6ce6..5e501a3d94168910e2ec8dd31440c3c0cd9e490a 100644
--- a/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Extensions/DocumentExtensions.cs
+++ b/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Extensions/DocumentExtensions.cs
@@ -41,6 +41,12 @@ public static async Task<SyntaxTree> GetRequiredSyntaxTreeAsync(this Document do
             return syntaxTree ?? throw new InvalidOperationException(string.Format(WorkspaceExtensionsResources.SyntaxTree_is_required_to_accomplish_the_task_but_is_not_supported_by_document_0, document.Name));
         }
 
+        public static SyntaxTree GetRequiredSyntaxTreeSynchronously(this Document document, CancellationToken cancellationToken)
+        {
+            var syntaxTree = document.GetSyntaxTreeSynchronously(cancellationToken);
+            return syntaxTree ?? throw new InvalidOperationException(string.Format(WorkspaceExtensionsResources.SyntaxTree_is_required_to_accomplish_the_task_but_is_not_supported_by_document_0, document.Name));
+        }
+
         public static async Task<SyntaxNode> GetRequiredSyntaxRootAsync(this Document document, CancellationToken cancellationToken)
         {
             var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);