code: func (s *ChangesService) SetTopic(changeID string, input *TopicInput) (*string, *Response, error) {
  	u := fmt.Sprintf("changes/%s/topic", changeID)
  
  	req, err := s.client.NewRequest("PUT", u, input)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	v := new(string)
  	resp, err := s.client.Do(req, v)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return v, resp, err
  }
docs: // SetTopic sets the topic of a change.
  // The new topic must be provided in the request body inside a TopicInput entity.
  //
  // Gerrit API docs: https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#set-topic