Throw on expected value.

src/Features/Core/Portable/ConvertTupleToStruct/AbstractConvertTupleToStructCodeRefactoringProvider.cs

-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System;
 using System.Collections.Generic;
@@ -345,10 +345,8 @@ private static string GetTitle(Scope scope)
                     return await GetDocumentsToUpdateForDependentProjectAsync(
                         document.Project, tupleType, cancellationToken).ConfigureAwait(false);
                 default:
-                    break;
+                    throw ExceptionUtilities.UnexpectedValue(scope);
             }
-
-            throw new NotImplementedException();
         }
 
         private async Task<ImmutableArray<DocumentToUpdate>> GetDocumentsToUpdateForDependentProjectAsync(