Merge pull request #30111 from dotnet/merges/dev15.9.x-to-dev16.0.x

Merge dev15.9.x to dev16.0.x

src/Features/Core/Portable/RemoveUnusedVariable/AbstractRemoveUnusedVariableCodeFixProvider.cs

@@ -32,7 +32,7 @@ internal abstract class AbstractRemoveUnusedVariableCodeFixProvider<TLocalDeclar
 
         public sealed override Task RegisterCodeFixesAsync(CodeFixContext context)
         {
-            Diagnostic diagnostic = context.Diagnostics.Single();
+            Diagnostic diagnostic = context.Diagnostics.First();
             context.RegisterCodeFix(new MyCodeAction(c => FixAsync(context.Document, diagnostic, c)), diagnostic);
             return Task.CompletedTask;
         }