【已解决】运行fastapi报错：TypeError: issubclass() arg 1 must be a class

在运行fastapi代码的时候，出现报错

Traceback (most recent call last):
  File "C:\Users\huqx2\AppData\Local\Programs\Python\Python39\lib\multiprocessing\process.py", line 315, in _bootstrap
    self.run()
  File "C:\Users\huqx2\AppData\Local\Programs\Python\Python39\lib\multiprocessing\process.py", line 108, in run
    self