docs: def _split_path(xj_path):
      """Extract the last piece of XJPath.
  
      :param str xj_path: A XJPath expression.
      :rtype: tuple[str|None, str]
      :return: A tuple where first element is a root XJPath and the second is
               a last piece of key.
      """
  
      res = xj_path.rsplit('.', 1)
      root_key = res[0]
      if len(res) > 1:
          return root_key, res[1]
      else:
          if root_key and root_key != '.':
              return None, root_key
          else:
              raise XJPathError('Path cannot be empty', (xj_path,))