Per PEP-8, the Python preferred-style is, "For sequences, (strings, lists, tuples), use the fact that empty sequences are false."

    Yes: if not seq:
        if seq:

    No: if len(seq):
        if not len(seq):

The Python libraries are not obliged to defend themselves against non-sensical types (i.e. defining an empty iterator as a subclass of list and returning a non-zero len).

I recommend leaving the code as-is and closing a "not a bug".  In a way, this report is no more interesting than observing that a __hash__ that returns a random value on each call doesn't work well in a dictionary.