When I using hibernate supports scala native collection library,I found PersistentCollection has same method empty, but have different return type.And my custom PersistentSet which referenced by custom UserCollectionType should implements scala.collection.mutable.Set and PersistentCollection simultaneously,so collision occurred.

/**
 * Is the collection empty? (don't try to initialize the collection)
 */
public boolean empty();

class PersistentSet(val session: SessionImplementor, var set: mutable.HashSet[Any] = null)  extends AbstractPersistentCollection with collection.mutable.Set[Any] {
}

I created a project hibernate-scala (https://github.com/beangle/hibernate-scala) support this integration. and it had supported scala native collection against my modified hibernate version.