code: func (t *TxStructure) HGet(key []byte, field []byte) ([]byte, error) {
  	dataKey := t.encodeHashDataKey(key, field)
  	value, err := t.reader.Get(dataKey)
  	if kv.ErrNotExist.Equal(err) {
  		err = nil
  	}
  	return value, errors.Trace(err)
  }
docs: // HGet gets the value of a hash field.