function wrap (payloads, cb) {
  var out = {};
  var count = Object.keys(payloads).length;

  return function (err, data) {
    // data: { topicName1: {}, topicName2: {} }
    if (err) return cb && cb(err);
    _.merge(out, data);
    count -= 1;
    // Waiting for all request return
    if (count !== 0) return;
    cb && cb(null, out);
  };
}