Saving the block is broken in Drupal 11.4

Thanks, RTBC as there are currently no other helpful validations:

  /**
   * {@inheritdoc}
   */
  public function blockValidate($form, FormStateInterface $form_state): void {
    $values = $form_state->getValues();
    if (!empty($values['add_active_trail_class'])) {
      return;
    }

    if ((int) $values['level'] !== 1 || (empty($values['expand_all_items']) && (int) $values['depth'] !== 1)) {
      $form_state->setError($form['menu_levels']['add_active_trail_class'], $this->t('"Add a CSS class to ancestors of the current page" is required if the menu if the initial is 1, or if menu items are not all expanded and the number of levels display is more than 1.'));
    }
  }

Hopefully this won't conflict with any submit values. I'm not even sure if it makes sense to extend SystemMenuBlock. I'll add a follow-up.

Here's the follow-up: #3610644: Check if extending SystemMenuBlock is helpful