def to_json(self):
        """
        :return: str
        """
        json_dict = self.to_json_basic()
        json_dict['sub_1'] = self.sub_address_1
        json_dict['sub_2'] = self.sub_address_2
        json_dict['sub_3'] = self.sub_address_3
        json_dict['sub_4'] = self.sub_address_4
        return json.dumps(json_dict)