code: func (t *Topic) UnmarshalJSON(input []byte) error {
  	topicbytes, err := hexutil.Decode(string(input[1 : len(input)-1]))
  	if err != nil {
  		return err
  	}
  	copy(t[:], topicbytes)
  	return nil
  }
docs: // MarshalJSON implements the json.Marshaler interface