老师，提交用户注册信息报错了，检查了代码，跟你讲的是一样的。请老师帮忙看看，到底那里有问题

AttributeError at /users/
'NoneType' object has no attribute 'username'
Request Method:	POST
Request URL:	http://127.0.0.1:9999/users/
Django Version:	3.1.1
Exception Type:	AttributeError
Exception Value:	
'NoneType' object has no attribute 'username'
Exception Location:	H:\Evns\MxShop\lib\site-packages\rest_framework_jwt\compat.py, line 35, in get_username
Python Executable:	H:\Evns\MxShop\Scripts\python3.8.exe
Python Version:	3.8.0
Python Path:	
['H:\\MxsShop',
 'H:\\MxsShop',
 'D:\\Program Files\\JetBrains\\PyCharm '
 '2019.2\\plugins\\python\\helpers\\pycharm_display',
 'H:\\Evns\\MxShop\\Scripts\\python38.zip',
 'd:\\python\\python38-32\\DLLs',
 'd:\\python\\python38-32\\lib',
 'd:\\python\\python38-32',
 'H:\\Evns\\MxShop',
 'H:\\Evns\\MxShop\\lib\\site-packages',
 'D:\\Program Files\\JetBrains\\PyCharm '
 '2019.2\\plugins\\python\\helpers\\pycharm_matplotlib_backend']
Server time:	Sun, 08 Nov 2020 12:33:07 +0800

	
Traceback (most recent call last):
  File "H:\Evns\MxShop\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "H:\Evns\MxShop\lib\site-packages\django\core\handlers\base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "H:\Evns\MxShop\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "H:\Evns\MxShop\lib\site-packages\rest_framework\viewsets.py", line 114, in view
    return self.dispatch(request, *args, **kwargs)
  File "H:\Evns\MxShop\lib\site-packages\rest_framework\views.py", line 505, in dispatch
    response = self.handle_exception(exc)
  File "H:\Evns\MxShop\lib\site-packages\rest_framework\views.py", line 465, in handle_exception
    self.raise_uncaught_exception(exc)
  File "H:\Evns\MxShop\lib\site-packages\rest_framework\views.py", line 476, in raise_uncaught_exception
    raise exc
  File "H:\Evns\MxShop\lib\site-packages\rest_framework\views.py", line 502, in dispatch
    response = handler(request, *args, **kwargs)
  File "H:\MxsShop\apps\users\views.py", line 79, in create
    payload = jwt_payload_handler(user)
  File "H:\Evns\MxShop\lib\site-packages\rest_framework_jwt\utils.py", line 34, in jwt_payload_handler
    username = get_username(user)
  File "H:\Evns\MxShop\lib\site-packages\rest_framework_jwt\compat.py", line 35, in get_username
    username = user.username
AttributeError: 'NoneType' object has no attribute 'username'