a number of robustness problems

[wyattscarpenter]

Many things give a nasty internal error message crash stack trace thing, when I suppose they should have a nice error message. Such as wyag commit with no -m

[thblt]

This is a tough one! It's always better to handle errors nicely, but that would complicate the code a lot. The stacktrace is ugly, but it gives the user a chance of understanding what happens.

The commit without -m thing is surprising though, I would expect argparse to fail nicely.