:param return_fields: tuple
        :raises: pybomb.exceptions.InvalidReturnFieldException

def _validate_return_fields(self, return_fields):
        """
        :param return_fields: tuple
        :raises: pybomb.exceptions.InvalidReturnFieldException
        """
        for return_field in return_fields:
            if return_field not in self.RESPONSE_FIELD_MAP:
                raise InvalidReturnFieldException(
                    '"{0}" is an invalid return field'.format(return_field)
                )