$ ./scripts/csv.py lfs.code.csv -bfunction -fsize -S
... blablabla ...
TypeError: cannot unpack non-iterable NoneType object
The issue was argparse's const defaults bypassing the type callback, so
the sort field ends up with None when it expects a tuple (well
technically a tuple tuple).
This is only an issue for csv.py because csv.py's sort fields can
contain exprs.