Throw exception for null listener in addEventListener

sky/engine/bindings/dart_event_listener.cc

Index: sky/engine/bindings/dart_event_listener.cc
diff --git a/sky/engine/bindings/dart_event_listener.cc b/sky/engine/bindings/dart_event_listener.cc
index 8f3835a09933605ef4222362411a4c9ddc911905..2c16f656c8efe62938fc3b3b3985d2cbf725984c 100644
--- a/sky/engine/bindings/dart_event_listener.cc
+++ b/sky/engine/bindings/dart_event_listener.cc
@@ -8,6 +8,7 @@
 #include "sky/engine/core/events/Event.h"
 #include "sky/engine/tonic/dart_api_scope.h"
 #include "sky/engine/tonic/dart_error.h"
+#include "sky/engine/tonic/dart_exception_factory.h"
 #include "sky/engine/tonic/dart_gc_visitor.h"
 #include "sky/engine/tonic/dart_isolate_scope.h"
 
@@ -66,4 +67,18 @@ void DartEventListener::Finalize(void* isolate_callback_data,
   listener->deref();  // Balances ref in DartEventListener::DartEventListener
 }
 
+PassRefPtr<EventListener>
+DartConverter<EventListener*>::FromArgumentsWithNullCheck(
+    Dart_NativeArguments args,
+    int index,
+    Dart_Handle& exception) {
+  Dart_Handle handle = Dart_GetNativeArgument(args, index);
+  if (Dart_IsNull(handle)) {
+    DartState* state = DartState::Current();
+    exception = state->exception_factory().CreateNullArgumentException(index);
+    return nullptr;
+  }
+  return FromDart(handle);
+}
+
 }  // namespace blink