I noticed that GIT_PREVIOUS_SUCCESSFUL_COMMIT was not set anymore on the Job that only builds our master branch. After some digging I found out that since the upgrade from the previous version (I can't find which version that was, is that stored somewhere?) the buildsByBranchName variable in any `build.xml` is not set anymore (it's empty). It is set in other jobs we have, just not this one.
This env is critical for us, so I'm going to try to rollback. I'm glad to help track down this problem if possible.