Grader error in C5_W4 Assignment

I am trying to solve the programming assignment - Transformers Architecture with Tensorflow
However, after submitting I got an error message like this.

" Cell #5. Can’t compile the student’s code. Error: TypeError(“unsupported operand type(s) for //: ‘NoneType’ and ‘int’”)"

How can I solve this problem?


First, be sure that you have completed the entire notebook before you submit it for grading.
You cannot submit a partially-completed assignment.