code: func (s *UsersService) Get(ctx context.Context, user string) (*User, *Response, error) {
  	var u string
  	if user != "" {
  		u = fmt.Sprintf("users/%v", user)
  	} else {
  		u = "user"
  	}
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	uResp := new(User)
  	resp, err := s.client.Do(ctx, req, uResp)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return uResp, resp, nil
  }
docs: // Get fetches a user. Passing the empty string will fetch the authenticated
  // user.
  //
  // GitHub API docs: https://developer.github.com/v3/users/#get-a-single-user
  // and: https://developer.github.com/v3/users/#get-the-authenticated-user