The following code from the org.jboss.errai.marshalling.client.marshallers.QualifyingMarshallerWrapper.doNotNullDemarshall() method throws a NullPointerException because o can be a GWTJSONValue, which means obj is null.

EJObject obj = o.isObject();
String objId = obj.get(SerializationParts.OBJECT_ID).isString().stringValue();