code: func (r *SegmentReader) initDocValuesProducers(codec Codec) error {
  	// var dir store.Directory
  	// if r.core.cfsReader != nil {
  	// 	dir = r.core.cfsReader
  	// } else {
  	// 	dir = r.si.Info.Dir
  	// }
  	// dvFormat := codec.DocValuesFormat()
  
  	// termsIndexDivisor := r.core.termsIndexDivisor
  	if !r.si.HasFieldUpdates() {
  		panic("not implemented yet")
  	}
  
  	panic("not implemented yet")
  }
docs: /* initialize the per-field DocValuesProducer */