def get_data_type(self):
        return db.Key
Data such as case properties can be referenced from reminder messages
dataset/ETHPy150Open jahlborn/appengine-rest-server/src/main/python/rest/__init__.py/BaseReferenceHandler.get_data_type--crossover with--dataset/ETHPy150Open dimagi/commcare-hq/corehq/apps/reminders/event_handlers.py/get_message_template_params