docs: def dumps(self, bucket=None):
          """Serialize files from a bucket.
  
          :param bucket: Instance of files
              :class:`invenio_files_rest.models.Bucket`. (Default:
              ``self.bucket``)
          :returns: List of serialized files.
          """
          return [
              self.file_cls(o, self.filesmap.get(o.key, {})).dumps()
              for o in sorted_files_from_bucket(bucket or self.bucket, self.keys)
          ]