Merge pull request #35831 from dibarbet/liveshare_fix_contained_document

Modify get contained document to accept null id as input.

src/VisualStudio/Core/Def/Implementation/Venus/ContainedDocument.cs

@@ -62,6 +62,11 @@ internal sealed partial class ContainedDocument : ForegroundThreadAffinitizedObj
 
         public static ContainedDocument TryGetContainedDocument(DocumentId id)
         {
+            if (id == null)
+            {
+                return null;
+            }
+
             ContainedDocument document;
             s_containedDocuments.TryGetValue(id, out document);
 

src/VisualStudio/Core/Test/Venus/ContainedDocumentTests.vb

+' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+Imports Microsoft.VisualStudio.LanguageServices.Implementation.Venus
+
+Namespace Microsoft.VisualStudio.LanguageServices.UnitTests.Venus
+    Public Class ContainedDocumentTests
+        <Fact>
+        Public Sub ContainedDocument_AcceptsNullInput()
+            Dim documentId = ContainedDocument.TryGetContainedDocument(Nothing)
+            Assert.Null(documentId)
+        End Sub
+    End Class
+End Namespace