Vaadin and JPA communication trouble

Hey there, I just tarted a vaadin project by vaadin’s youtube tutorial series, and i have a problem with jpa connection. I created my objects, as on the image and all object has a repository class extends class specific JpaRepository and each of them has a service, but i want to add “Nyelvtudás” objects in “SzemélyService” class. However if i do it, like in the commented segment, then it didnt add nyelvtudás, and if I call fetchAll() method the hole thing crashes. I couldn’t find any solution, or better tuts, so if someone could tell me hwats worg i would be very thanksfull.

The relation of the objects: i want to store many custom “Nyelvtudás” object" in “Személy” object’s “private List<Nyelvtudás> nyelvtudás” field. Each “Személy” should have different and different “Nyelvtudás”.