Plugins must return render arrays

Now in D8 basically all plugin types have to return a render array instead of a string. For example if you have an Area Handler in
d7 it looked like:

  function render($empty) {
    $build = array(
      '#type' => 'links',
      // ...
    );
    return drupal_render($build);
  }

In D8 you can directly return the array:

  public function render($empty) {
    return array(
      '#type' => 'links',
      // ...
    );
  }