I'm using v1.3.0 and this error was from the second commit, in which no valid revision could be found.
See the log here. Looks to me like the ^1 after the fist hash is not valid in the case of there only being 2 commits. I haven't looked ad the code but why would you need to get the previous commit from the last known commit before the push?

The first commit worked correctly, but it detected an invalid commit message due to that commit being generated by GitHub and not valid style.