code: function () {
              if (this._content) {
                  var error = new gpf.Error.InvalidCSV();
                  this._setReadError(error);
                  return Promise.reject(error);
              }
              this._completeReadBuffer();
              return Promise.resolve();
          }
docs: endregion region gpf.interfaces.IFlushableStream 
  @gpf:sameas gpf.interfaces.IFlushableStream#flush
  @since 0.2.3