Grader error: 'NoneType' object is not subscriptable

I get 0 score due to error:
There was a problem compiling the code from your notebook. Details:
‘NoneType’ object is not subscriptable

The assignment works when I run it and returns expected result Not sure where that comes from. Can you please help me find which line is causing issue?

Does this help?

Yes. I got a new notebook and it worked. I don’t know what do I keep doing to break it, but anyways thanks again.