I agree this should be closed (and I'm closing it). I don't see any reason why this function should do something other than raise TypeError if given bs=None. If you want that behavior, write a small wrapper function.

The "if not bs" check appears to be an optimization for the case of zero-length input. Hopefully the code would continue to work without that test (or instead testing for len(bs)==0), but in my opinion it's not worth the risk of removing or changing it.