can't undo initial changes to codebase

[aryairani]

The change we made such that cons b (one empty) == one b makes it so that you can't undo the first change made to the root, which I guess I found counterintuitive, even though that is arguably the way git works.

In other words, if the first thing I do in a new codebase is a pull, I can no longer undo the pull. I can still use reflog to revert it, though.

What were some of the alternative solutions we had considered?

/cc @pchiusano

[aryairani]

We could special-case undo to use Branch.empty when trying to undo a One.