Hello @MalteR, nice to meet you.
I didn't use spring in the last year but I think that probably you've to try this solution from @gerrit.meier.
Check if your using correctly native types, please.
If that is operative and not work as expected, I will help you in other way (I've to create a little test before, so I'll need some hours and tomorrow I'll be a lot busy, so I'll try in weekend).