def get_referenced_user(self):
        """
        :rtype: BunqModel
        """

        if self._user_person is not None:
            return self._user_person

        if self._user_company is not None:
            return self._user_company

        if self._user_api_key is not None:
            return self._user_api_key

        raise BunqException(self._ERROR_ALL_FIELD_IS_NULL)