Merge pull request #25225 from Neme12/concatToInterpolatedString

Fixing NullReferenceException inside ConvertToInterpolatedString

src/EditorFeatures/CSharpTest/ConvertToInterpolatedString/ConvertConcatenationToInterpolatedStringTests.cs

@@ -398,6 +398,36 @@ void M()
     {
         var v = ""A"" + 1 + [||]""B"" + @""C"";
     }
+}");
+        }
+
+        [WorkItem(20943, "https://github.com/dotnet/roslyn/issues/20943")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsConvertToInterpolatedString)]
+        public async Task TestMissingWithDynamic1()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"class C
+{
+    void M()
+    {
+        dynamic a = ""b"";
+        string c = [||]""d"" + a + ""e"";
+    }
+}");
+        }
+
+        [WorkItem(20943, "https://github.com/dotnet/roslyn/issues/20943")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsConvertToInterpolatedString)]
+        public async Task TestMissingWithDynamic2()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"class C
+{
+    void M()
+    {
+        dynamic dynamic = null;
+        var x = dynamic.someVal + [||]"" $"";
+    }
 }");
         }
     }

src/Features/Core/Portable/ConvertToInterpolatedString/AbstractConvertConcatenationToInterpolatedStringRefactoringProvider.cs

@@ -190,9 +190,9 @@ private static SyntaxNode ConcatinateTextToTextNode(SyntaxGenerator generator, S
                 return false;
             }
 
-            var method = semanticModel.GetSymbolInfo(expression, cancellationToken).Symbol as IMethodSymbol;
-            return method?.MethodKind == MethodKind.BuiltinOperator &&
-                   method.ContainingType.SpecialType == SpecialType.System_String &&
+            return semanticModel.GetSymbolInfo(expression, cancellationToken).Symbol is IMethodSymbol method &&
+                   method.MethodKind == MethodKind.BuiltinOperator &&
+                   method.ContainingType?.SpecialType == SpecialType.System_String &&
                    (method.MetadataName == WellKnownMemberNames.AdditionOperatorName ||
                     method.MetadataName == WellKnownMemberNames.ConcatenateOperatorName);
         }