bpython quits when parsing empty arguments with argparse module

bfrascher

I was testing around some things with the argparse module in bpython when suddenly bpython quit on me with error code 1. I tried to break the problem down and the code below seems to be the minimal reproducer:

$ bpython
bpython version 0.17.1 on top of Python 3.7.0 /usr/bin/python
>>> import argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('foo')
_StoreAction(option_strings=[], dest='foo', nargs=None, const=None, default=None, type=None, choices=None, help=None, metavar=None)
>>> parser.parse_args()
usage: bpython [-h] foo
>>> parser.parse_args()
(2,)
$ echo $?
1

The second parser.parse_args() is not entered by me, but appears automatically on executing the first parser.parse_args() line.