It looks like choices are broken for nargs='*' even without using default:

>>> import argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('test', nargs='*', choices=['foo', 'bar', 'baz'])
_StoreAction(option_strings=[], dest='test', nargs='*', const=None, default=None, type=None, choices=['foo', 'bar', 'baz'], help=None, metavar=None)
>>> parser.parse_args([])
usage: [-h] [{foo,bar,baz} [{foo,bar,baz} ...]]
: error: argument test: invalid choice: [] (choose from 'foo', 'bar', 'baz')