code: function(job, batchId) {
    Batch.super_.call(this, { objectMode: true });
    this.job = job;
    this.id = batchId;
    this._bulk = job._bulk;
    this._deferred = Promise.defer();
    this._setupDataStreams();
  }
docs: /*-------------------------------------------- 
  Batch (extends RecordStream)
  
  @protected
  @class Bulk~Batch
  @extends {stream.Writable}
  @implements {Promise.<Array.<RecordResult>>}
  @param {Bulk~Job} job - Bulk job object
  @param {String} [batchId] - Batch ID (if already available)