docs: function MapReduce(query, callback, stream) {
      CommandBase.call(this, 'RpbMapRedReq', 'RpbMapRedResp', callback);
      var options = { query: query, stream: stream };
      this.validateOptions(options, schema);
      this.query = this.options.query;
      this.stream = this.options.stream;
      if (!this.stream) {
          this.response = {};
      }
  }