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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.