criteria api sub-select with sub-select and custom fields - jpa

Question

I'd like to rewrite following sql query to criteria api:
select * from demands d
where exists (
select * from (
select a.demandid,
min(coalesce(a.securitylevel, a.securitylevel, -1)) themin,
max(coalesce(a.securitylevel, -1)) themax
from allocations a
group by demandid)
where demandid = d.id
and (themin = -1 and themax = -1
or themax >= 5)
);
The problem is that I'm not able to figure out how to write select clause for sub-queries, my current implementation produces CompoundSelection however subQyer.select accepts only Expression (DemandSecLevel is custom POJO/DTO).
public static Specification<Demand> bySecurityLevel(
final Integer securityLevel) {
return (root, query, cb) -> {
final Subquery<DemandSecLevel> subQuery = query.subquery(DemandSecLevel.class);
final Root<AllocationEntry> allocationEntryRoot = subQuery.from(AllocationEntry.class);
subQuery.select(cb.construct(
DemandSecLevel.class,
allocationEntryRoot.get(AllocationEntry_.incidentDemandId),
cb.min(cb.coalesce(allocationEntryRoot.get(AllocationEntry_.securityLevel), -1))
.alias("minSecLevel"),
cb.max(cb.coalesce(allocationEntryRoot.get(AllocationEntry_.securityLevel), -1))
.alias("maxSecLevel")
));