code: func (db *DB) HDump(key []byte) ([]byte, error) {
  	v, err := db.HGetAll(key)
  	if err != nil {
  		return nil, err
  	} else if len(v) == 0 {
  		return nil, err
  	}
  
  	o := make(rdb.Hash, len(v))
  	for i := 0; i < len(v); i++ {
  		o[i].Field = v[i].Field
  		o[i].Value = v[i].Value
  	}
  
  	return rdb.Dump(o)
  }
docs: // HDump dumps the hash value of key