code: func (t *TxStructure) HSet(key []byte, field []byte, value []byte) error {
  	if t.readWriter == nil {
  		return errWriteOnSnapshot
  	}
  	return t.updateHash(key, field, func([]byte) ([]byte, error) {
  		return value, nil
  	})
  }
docs: // HSet sets the string value of a hash field.