magit/magit — comment on commit b2daab99f849ab6d9a7d2f40b76054eb67f9ed9a
File:  line 0
By pjweisberg:

It also breaks the ability to merge in another branch and manually discard all of its changes. (I.e., you can't commit if the merge result turns out being identical to the previous HEAD.) That's even more useful.

And I don't think there's a way to toggle "allow-empty" without popping up the log-edit window *first*.