protected function prepareFiles($files) {
    $values = [];

    foreach ($files as $file_uuid) {
      $file = $this->fileStorage->loadByProperties([
        'uuid' => $file_uuid,
      ]);

      if ($file) {
        $values[] = [
          'target_id' => current($file)->id(),
        ];
      }
    }

    return $values;
  }