code: func (s *AccountsService) SetUsername(accountID string, input *UsernameInput) (*string, *Response, error) {
  	u := fmt.Sprintf("accounts/%s/username", accountID)
  
  	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: // SetUsername sets a new username.
  // The new username must be provided in the request body inside a UsernameInput entity.
  // Once set, the username cannot be changed or deleted.
  // If attempted this fails with “405 Method Not Allowed”.
  //
  // As response the new username is returned.
  //
  // Gerrit API docs: https://gerrit-review.googlesource.com/Documentation/rest-api-accounts.html#set-username