C1W2_Assignment Assignment 1 Error

Hi all, any help here? When I run the test (w2_unittest.test_row_echelon_form(row_echelon_form)) for exercise 1, the output is “All tests passed”. However, when I submit the notebook for grading, it gives me 0 grade saying “Unable to find object required for grading in your code.”

Would appreciate your help!