Week 1 assignment got: <class 'NoneType'> error

I don’t know why this error is popping up

output from my code matches the expected results. I submitted multiple times, rebooted the server, used the get latest version option. None of them are working. Unable to pass this assignment because of this error

Please check notebook metadata and refresh the workspace if required / in doubt. If that doesn’t help, please click my name and message your notebook as an attachment.