public function getSourceFieldName($media_type) {
    $bundle = $this->entityTypeManager->getStorage('media_type')->load($media_type);
    if (!$bundle) {
      throw new NotFoundHttpException("Bundle $media_type does not exist");
    }

    $type_configuration = $bundle->get('source_configuration');
    if (!isset($type_configuration['source_field'])) {
      return NULL;
    }

    return $type_configuration['source_field'];
  }