code: def _next_dir_gen(self, root):
      
      for e in root.getiterator(common._T_COMMON_PREFIXES):
        yield common.GCSFileStat(
            self._path + '/' + e.find(common._T_PREFIX).text,
            st_size=None, etag=None, st_ctime=None, is_dir=True)
        e.clear()
      yield None
docs: Generator for next directory element in the document.
  
      Args:
        root: root element in the XML tree.
  
      Yields:
        GCSFileStat for the next directory.