code: func (s *seriesIteratorAdapter) Next() (tsdb.SeriesElem, error) {
  	if s.itr == nil {
  		return nil, nil
  	}
  
  	row, err := s.itr.Next()
  	if err != nil {
  		return nil, err
  	}
  
  	if row == nil {
  		return nil, nil
  	}
  
  	s.ea.name = row.Name
  	s.ea.tags = row.Tags
  	return s.elem, nil
  }
docs: // Next returns the next tsdb.SeriesElem.
  //
  // The returned tsdb.SeriesElem is valid for use until Next is called again.