Issue #3300160 by Rhezios: Call to undefined method...

  }

  /**

   * If the current node is a course object, fulfill it for the current user.

   * Copy questions to a new quiz revision.

   *

   * @param ReplicateEntityEvent $event

   * @param AfterSaveEvent $event

   */

  public function afterSave(AfterSaveEvent $event) {

    /* @var $quiz Quiz */

    $quiz = $event->getEntity();

    $entity = $event->getEntity();

    if ($entity->getEntityTypeId() == 'quiz') {

      $old_quiz = Drupal::entityTypeManager()

        ->getStorage('quiz')

      ->loadRevision($quiz->old_vid);

    $quiz->copyFromRevision($old_quiz);

        ->loadRevision($entity->old_vid);

      $entity->copyFromRevision($old_quiz);

    }

  }

}