For each project in GitLab I have two jobs: one for branch master and the other for branch called develop (even if that branch does not exists because it will in future). I use the branch filter option to chose when to build each job depending on the branch that has recieved the push. I create those jobs using JobDSL plugin so branch name is put directly on XML when the job is created.

When both branches exist it works fine. But when the branch develop does not exists and a push is made to master, both jobs ( master and develop ) starts to build.