I don't have the code in front of me but is args['system_user'] assured? If 'system_user' isn't in the args dict then it too will throw a KeyError.
Yes, it's guaranteed, defaults to ipsilon
parser.add_argument('--system-user', default='ipsilon',
OK, ACK then.
(note: this has been merged with Rob's ack. Had to hit the Close button because of a bug in Pagure).