JPA Criteria Query distinct

I got it. The problem was my CriteraQuery needed to be of type String. This works:

CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<String> query = builder.createQuery(String.class);
Root<RuleVar> ruleVariableRoot = query.from(RuleVar.class);
query.select(ruleVariableRoot.get(RuleVar_.varType)).distinct(true);