C2_W1_Assignment: functions are of the wrong type

Hi, I’m having trouble understanding the error of my functions and why they are not passing the test. On google colab notebook, I’m getting the right outputs for the graded functions. The reason why my functions are not passing is explained as follows:
Details of failed tests for create_train_val_dirs

Failed test case: create_train_val_dirs has incorrect type.
Expected:
typing.Callable,
but got:
<class ‘NoneType’>.

Details of failed tests for split_data

Failed test case: split_data has incorrect type.
Expected:
typing.Callable,
but got:
<class ‘NoneType’>.

Details of failed tests for train_val_generators

Failed test case: train_val_generators has incorrect type.
Expected:
typing.Callable,
but got:
<class ‘NoneType’>.

Details of failed tests for create_model

Failed test case: create_model has incorrect type.
Expected:
typing.Callable,
but got:
<class ‘NoneType’>.

Could you explain the error and how can I check for it in the notebook itself? Thanks

Never mind, it worked when I submitted the code again today. However, it didn’t work last few times I submitted it, and I don’t know why.