ParentNode#appendChild(null) shouldn't crash

sky/engine/tonic/dart_wrappable.cc

Index: sky/engine/tonic/dart_wrappable.cc
diff --git a/sky/engine/tonic/dart_wrappable.cc b/sky/engine/tonic/dart_wrappable.cc
index 1bf69d4cf5b023ba6101340539b1f5c3b40edcde..a7ab0d2f9bc52331593a8266fc47882a19569087 100644
--- a/sky/engine/tonic/dart_wrappable.cc
+++ b/sky/engine/tonic/dart_wrappable.cc
@@ -7,8 +7,10 @@
 
 #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 {
 
@@ -74,9 +76,17 @@ DartWrappable* DartConverterWrappable::FromArguments(Dart_NativeArguments args,
 
 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);