ParentNode#appendChild(null) shouldn't crash

sky/engine/tonic/dart_wrappable.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/tonic/dart_wrappable.h"
 
 #include "sky/engine/tonic/dart_class_library.h"
 #include "sky/engine/tonic/dart_error.h"
+#include "sky/engine/tonic/dart_exception_factory.h"
 #include "sky/engine/tonic/dart_state.h"
 #include "sky/engine/tonic/dart_wrapper_info.h"
+#include "sky/engine/wtf/text/StringBuilder.h"
 
 namespace blink {
 
 DartWrappable::~DartWrappable() {
   CHECK(!dart_wrapper_);
 }
 
 void DartWrappable::AcceptDartGCVisitor(DartGCVisitor& visitor) const {
 }
 
@@ skipping 45 matching lines @@
   if (Dart_IsError(result)) {
     exception = Dart_NewStringFromCString(DartError::kInvalidArgument);
     return nullptr;
   }
   return reinterpret_cast<DartWrappable*>(
       native_fields[DartWrappable::kPeerIndex]);
 }
 
 DartWrappable* DartConverterWrappable::FromArgumentsWithNullCheck(
     Dart_NativeArguments args, int index, Dart_Handle& exception) {
-    Dart_Handle handle = Dart_GetNativeArgument(args, index);
-  if (Dart_IsNull(handle))
+  Dart_Handle handle = Dart_GetNativeArgument(args, index);
+  if (Dart_IsNull(handle)) {
+    DartState* state = DartState::Current();
+    StringBuilder message;
+    message.appendLiteral("Argument ");
+    message.appendNumber(index);
+    message.appendLiteral(" cannot be null.");
+    exception = state->exception_factory().CreateException("ArgumentError",
+                                                           message.toString());
     return nullptr;
+  }
   intptr_t native_fields[DartWrappable::kNumberOfNativeFields];
   Dart_Handle result = Dart_GetNativeFieldsOfArgument(
       args, index, DartWrappable::kNumberOfNativeFields, native_fields);
   if (Dart_IsError(result)) {
     exception = Dart_NewStringFromCString(DartError::kInvalidArgument);
     return nullptr;
   }
   return reinterpret_cast<DartWrappable*>(
       native_fields[DartWrappable::kPeerIndex]);
 }
 
 }  // namespace blink