code: function autoSeriesName(seriesModel) {
      // User specified name has higher priority, otherwise it may cause
      // series can not be queried unexpectedly.
      var name = seriesModel.name;
      if (!modelUtil.isNameSpecified(seriesModel)) {
          seriesModel.name = getSeriesAutoName(seriesModel) || name;
      }
  }
docs: MUST be called after `prepareSource` called
  Here we need to make auto series, especially for auto legend. But we
  do not modify series.name in option to avoid side effects.