I doubt they even exist as a club. I didn't see them on TV last season when watching the Champions League or Europa League matches in March. In fact I'm not even sure it exists as a City. Have you been there?
No-one's been there. I've even checked with two people I know studying at the big university there. They've confirmed that:
a) The town doesn't exist.
b) If it did exist, it wouldn't have a football team.
c) Even if it did, it never had a goalkeeper.
d
d) If there had been a goalkeeper, he only would have played well because of VVD...
e) Who was obviously never there, because a).
The whole Mainz thing was basically made up by Klopp to buff his CV for the Dortmund job. Everybody knows you can't get anywhere in Germany with gaps on your CV.