Could you post a link to the implementation?
I’m currently not sure, if Module refers to nn.Module or a custom implementation in FastAI.
Of course removing all undefined variables, works fine:
class TabularModel(nn.Module):
    "Basic model for tabular data."
    def __init__(self):
        super().__init__()
        b = 0
        assert b != 0, 'test'      

To debug this issue, we would need an executable code snippet.