docs: def sorted_files_from_bucket(bucket, keys=None):
      """Return files from bucket sorted by given keys.
  
      :param bucket: :class:`~invenio_files_rest.models.Bucket` containing the
          files.
      :param keys: Keys order to be used.
      :returns: Sorted list of bucket items.
      """
      keys = keys or []
      total = len(keys)
      sortby = dict(zip(keys, range(total)))
      values = ObjectVersion.get_by_bucket(bucket).all()
      return sorted(values, key=lambda x: sortby.get(x.key, total))