code: func (txops txOps) applyMetadata(ns, coll string, metadataWrite *kvrwset.KVMetadataWrite) error {
  	if metadataWrite.Entries == nil {
  		txops.metadataDelete(compositeKey{ns, coll, metadataWrite.Key})
  	} else {
  		metadataBytes, err := storageutil.SerializeMetadata(metadataWrite.Entries)
  		if err != nil {
  			return err
  		}
  		txops.metadataUpdate(compositeKey{ns, coll, metadataWrite.Key}, metadataBytes)
  	}
  	return nil
  }
docs: // applyMetadata records updatation/deletion of a metadataWrite