CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Flow> criteriaQuery = criteriaBuilder
      .createQuery(Flow.class);
Root<Flow> root = criteriaQuery.from(Flow.class);
criteriaQuery.select(root.alias("flow"));

List<Predicate> predicates = new ArrayList<Predicate>();
predicates.add(criteriaBuilder.equal(
      root.get("componentTypeReference"),
      flow.getComponentTypeReference()));
predicates.add(criteriaBuilder.equal(
      root.<ProductionCategory> get("productionCategory"),
      flow.getProductionCategory()));
predicates.add(criteriaBuilder.equal(root.<Device> get("device"),
      flow.getDevice()));
Set<Date> optimalPrintingDates = flow.getOptimalPrintingDates();
if (optimalPrintingDates != null) {
   Path<Set<Date>> optimalPrintingDatesPath = root
         .<Set<Date>> get("optimalPrintingDates");
   if (optimalPrintingDates.isEmpty()) {
      predicates.add(criteriaBuilder
            .isEmpty(optimalPrintingDatesPath));   // this makes Hibernate fail
   } else {
      predicates.add(criteriaBuilder.equal(optimalPrintingDatesPath,
            flow.getOptimalPrintingDates()));
   }
}
Set<Priority> priorities = flow.getPriorities();
if (priorities != null) {
   Path<Set<Priority>> prioritiesPath = root
         .<Set<Priority>> get("priorities");
   if (priorities.isEmpty()) {
      predicates.add(criteriaBuilder.isEmpty(prioritiesPath));  // this makes Hibernate fail
   } else {
      predicates.add(criteriaBuilder.equal(prioritiesPath,
            flow.getPriorities()));
   }
}

criteriaQuery.where(predicates.toArray(new Predicate[0]));
TypedQuery<Flow> singleFlowQuery = entityManager
      .createQuery(criteriaQuery);
List<Flow> foundFlows = singleFlowQuery.getResultList();
if (foundFlows == null || foundFlows.isEmpty()) {
   return null;
} else if (foundFlows.size() > 1) {
   throw new NonUniqueResultException("Le flux n'est pas unique : "
         + foundFlows.size());
} else {
   return foundFlows.get(0);
}

Expression<Integer> dateCount = criteriaBuilder
      .size(optimalPrintingDatesPath);
predicates.add(criteriaBuilder.equal(dateCount, 0));