The "Known Limitations / Bugs" section on https://wiki.jenkins-ci.org/display/JENKINS/Git+Parameter+Plugin mentions:

There is a problem when you want to build your project for a first time and you don't have any suitable workspace which works with git, then the list to chose from is empty, but it will work after the first build

This is true for a single node Jenkins setup, but if building on slaves then the git checkout/repos usually is present only on the slaves and the 'git fetch -t' by the git parameter plugin will never succeed.