code: function finisher(error, output, callback)
  {
    // signal end of the stream
    // only for successfully finished streams
    if (!error)
    {
      this.push(null);
    }
  
    // back to original track
    callback(error, output);
  }
docs: Stream wrapper for finishing callback
  
  @this  ReadableAsyncKit#
  @param {mixed} error - error response
  @param {mixed} output - iterator output
  @param {function} callback - callback that expects final results