我无法再运行 kivy，我已经尝试了一切，卸载了 pycharm 并且它不起作用

Question

from kivy.app import App
from kivy.uix.button import Button


class KVvsPY(App):
    def build(self):
        return Button(text='ok')


janela = KVvsPY()
janela.run()

这是代码，非常简单，因为它有一个我不知道如何解决的错误

这是错误

Traceback (most recent call last):
   File "C:\Users\Computador\PycharmProjects\pythonProject2\main.py", line 11, in <module>
     janela.run()
   File "C:\Users\Computador\PycharmProjects\pythonProject2\venv\lib\site-packages\kivy\app.py", line 954, in run
     self._run_prepare()
   File "C:\Users\Computador\PycharmProjects\pythonProject2\venv\lib\site-packages\kivy\app.py", line 932, in _run_prepare
     Window.add_widget(self.root)
 AttributeError: 'NoneType' object has no attribute 'add_widget'

Process finished with exit code 1