docs: def marker_for_line(self, line):
          """
          Returns the marker that is displayed at the specified line number if
          any.
  
          :param line: The marker line.
  
          :return: Marker of None
          :rtype: pyqode.core.Marker
          """
          block = self.editor.document().findBlockByNumber(line)
          try:
              return block.userData().messages
          except AttributeError:
              return []