关于argument of type 'NoneType' is not iterable的提问

[Everchener]

[ERROR] nonebot | Error when running RunPreProcessors. Running cancelled!
Traceback (most recent call last):
  File "d:\python395\lib\site-packages\nonebot\message.py", line 146, in _check_matcher
    await _run_matcher(Matcher, bot, event, state, stack, dependency_cache)
> File "d:\python395\lib\site-packages\nonebot\message.py", line 179, in _run_matcher
    await asyncio.gather(*coros)
  File "d:\python395\lib\site-packages\nonebot\utils.py", line 138, in run_coro_with_catch
    return await coro
  File "d:\python395\lib\site-packages\nonebot\dependencies\__init__.py", line 92, in __call__
    return await self.call(**values)
  File "d:\python395\lib\site-packages\nonebot_plugin_manager\__init__.py", line 41, in _
    plugin_manager.update_plugin(
  File "d:\python395\lib\site-packages\nonebot_plugin_manager\manager.py", line 106, in update_plugin
    other = PluginManager().__add_plugin(plugin).__remove_plugin(plugin)
  File "d:\python395\lib\site-packages\nonebot_plugin_manager\manager.py", line 116, in __add_plugin
    if p not in self.__plugin_list:
TypeError: argument of type 'NoneType' is not iterable

python版本为3.9.5，之前使用BOT的时候没问题，有一天突然出了问题，将其它插件关闭后调用/echo指令也会出这样的错误，重装脚手架和BOT似乎都仍然会出现这样的问题，请问怎样才能解决这个问题呢？

[yanyongyu]

@j1g5awi