When using UserType there are other issue.
When you do an Insert or an Update, #nullSafeSet receives (in my case) a Set which is converted to a string, but when the query being bind, that method receives a string, even when i set a Set as query parameter, so it breaks due to ClassCast.

java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Set

at org.fgaule.TeamUserType.nullSafeSet(TeamUserType.java:50)

    Set<String> a = new HashSet<String>();
        a.add("CAI");
        q.where(cb.equal(c.get("foes"), a));

I'm attaching those test cases too.