Handlify callers of Object::GetElement.

src/json-stringifier.h

Index: src/json-stringifier.h
diff --git a/src/json-stringifier.h b/src/json-stringifier.h
index 4510c4b45b65b9b8c18079a46e901d69eb4a355f..175b9a16c76812f7950418985cc15cf63fcd8ce8 100644
--- a/src/json-stringifier.h
+++ b/src/json-stringifier.h
@@ -655,7 +655,7 @@ BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSObject(
                        isolate_);
       } else {
         property = GetProperty(isolate_, object, key);
-        if (property.is_null()) return EXCEPTION;
+        RETURN_IF_EMPTY_HANDLE_VALUE(isolate_, property, EXCEPTION);
       }
       Result result = SerializeProperty(property, comma, key);
       if (!comma && result == SUCCESS) comma = true;
@@ -687,7 +687,7 @@ BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSObject(
           property = GetProperty(isolate_, object, key_handle);
         }
       }
-      if (property.is_null()) return EXCEPTION;
+      RETURN_IF_EMPTY_HANDLE_VALUE(isolate_, property, EXCEPTION);
       Result result = SerializeProperty(property, comma, key_handle);
       if (!comma && result == SUCCESS) comma = true;
       if (result >= EXCEPTION) return result;