code: func (t *TxStructure) HClear(key []byte) error {
  	metaKey := t.encodeHashMetaKey(key)
  	meta, err := t.loadHashMeta(metaKey)
  	if err != nil || meta.IsEmpty() {
  		return errors.Trace(err)
  	}
  
  	err = t.iterateHash(key, func(field []byte, value []byte) error {
  		k := t.encodeHashDataKey(key, field)
  		return errors.Trace(t.readWriter.Delete(k))
  	})
  
  	if err != nil {
  		return errors.Trace(err)
  	}
  
  	return errors.Trace(t.readWriter.Delete(metaKey))
  }
docs: // HClear removes the hash value of the key.