def METHOD_NAME(self):
    diff_results = [(k, self.meta(k).diff_result) for k in self._data]
    diff_results = [dr for dr in diff_results if dr[1] is not None]
    if diff_results:
        before = dict((dr[0], dr[1]['before']) for dr in diff_results)
        after = dict((dr[0], dr[1]['after']) for dr in diff_results)
        return {'before': before, 'after': after}
    return None