We are using an environment variable set by this plugin in the Maven command line. Ever since that commit these variables are not set anymore.
The problem is that ConfigFileBuildWrapper doesn't return an Environment anymore but registers an action instead which then in turn should register the environment variables. Unfortunately MavenModuleSetBuild only takes the returned Environments from BuildWrapper into account but not those from actions registered by them.
I can fix this by reverting part of the commit mentioned above. This is the first time I've ever dug into Jenkins' code so there might be a simpler solution or this might even be a bug in Jenkins itself. I'm not sure.
I'll attach this simplistic patch but I'm happy to try to work on a better one if given instructions.