public function getRecipientOrganizerFromEntity(array $related_entity, array $data) {
    $recipients = [];

    // Don't return recipients if user comments on own content.
    $original_related_object = $data['related_object'][0];
    if (isset($original_related_object['target_type'])
      && $original_related_object['target_type'] === 'event_enrollment'
      && $related_entity !== NULL) {
      $storage = \Drupal::entityTypeManager()->getStorage($related_entity['target_type']);
      $event = $storage->load($related_entity['target_id']);

      if ($event === NULL) {
        return $recipients;
      }

      $recipients[] = [
        'target_type' => 'user',
        'target_id' => $event->getOwnerId(),
      ];
    }

    // If there are any others we should add. Make them also part of the
    // recipients array.
    \Drupal::moduleHandler()
      ->alter('activity_recipient_organizer', $recipients, $event);

    return $recipients;
  }