code: public Optional<User> getOptionalUser(String username) {
          try {
              return (Optional.ofNullable(getUser(username)));
          } catch (GitLabApiException glae) {
              return (GitLabApi.createOptionalFromException(glae));
          }
      }
docs: Lookup a user by username and return an Optional instance.
  
  <p>NOTE: This is for admin users only.</p>
  
  <pre><code>GitLab Endpoint: GET /users?username=:username</code></pre>
  
  @param username the username of the user to get
  @return the User for the specified username as an Optional instance