'Asynchronous Rollback operation.
Args:
config: A Configuration object or None.  Defaults are taken from
the connection\'s default configuration.
Returns:
A MultiRpc object.'

def async_rollback(self, config):

    transaction = self._end_transaction()
    if (transaction is None):
        return None
    if (self._api_version == _CLOUD_DATASTORE_V1):
        req = googledatastore.RollbackRequest()
        req.transaction = transaction
        resp = googledatastore.RollbackResponse()
    else:
        req = transaction
        resp = api_base_pb.VoidProto()
    return self._make_rpc_call(config, 'Rollback', req, resp, get_result_hook=self.__rollback_hook, service_name=self._api_version)
