def METHOD_NAME(self, file_basename: Union[str, List[str]]):
    if isinstance(file_basename, str):
        return os.path.join(self.get_site_config_dir(), file_basename)
    elif isinstance(file_basename, list):
        return self._fallback_path(file_basename)
    else:
        raise ValueError(f"invalid file_basename '{file_basename}': must be str or List[str]")