/**
  * Get the revision owner for an ContentEntity.
  *
  * Need because 2 possible interfaces support this.
  *
  * @param \Drupal\Core\Entity\ContentEntityInterface $entity
  *
  * @return \Drupal\user\UserInterface|NULL
  */
 protected function getRevisionOwner(ContentEntityInterface $entity)
 {
     if ($entity instanceof NodeInterface) {
         return $entity->getRevisionAuthor();
     } elseif ($this->implementsInterface($entity, ['Drupal\\entity\\Revision\\EntityRevisionLogInterface'])) {
         /** @var \Drupal\entity\Revision\EntityRevisionLogInterface $entity */
         return $entity->getRevisionUser();
     }
     return NULL;
 }