code: func (itr *seriesQueryAdapterIterator) Next() (*query.FloatPoint, error) {
  	for {
  		// Read next series element.
  		e, err := itr.itr.Next()
  		if err != nil {
  			return nil, err
  		} else if e.SeriesID.IsZero() {
  			return nil, nil
  		}
  
  		// Skip if key has been tombstoned.
  		seriesKey := itr.sfile.SeriesKey(e.SeriesID)
  		if len(seriesKey) == 0 {
  			continue
  		}
  
  		// Convert to a key.
  		name, tags := ParseSeriesKey(seriesKey)
  		key := string(models.MakeKey(name, tags))
  
  		// Write auxiliary fields.
  		for i, f := range itr.opt.Aux {
  			switch f.Val {
  			case "key":
  				itr.point.Aux[i] = key
  			}
  		}
  		return &itr.point, nil
  	}
  }
docs: // Next emits the next point in the iterator.