Cannot use Specification<T> interface to create subquery predicates

I implemented numerous own Specification classes that implement the interface called Specification<T> in the org.springframework.data.jpa.domain package. This Specification<T> interface has a Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder); interface function which has to be implemented along with implementing the interface. This toPredicate function has 3 parameters, the Root<T>, the CriteriaQuery<?>, and the Criteriabuilder. As long as I want to create the Predicate object for a CriteriaQuery object it works fine. However I have cases, when I would like to use my own Specification classes to create Predicate objects for subqueries. As I have found out this is currently impossible because the toPredicate function requires CriteriaQuery object as its second parameter instead of requiring the common parent of CriteriaQuery<T> and Subquery<T> that could be AbstractQuery<T>. It would be nice if Specification<T> interface could be used to create Predicate objects for subqueries too. Right now I have to duplicate the code written in my own Specification classes if I would like to use it for subquery predicates.

Start with the Specification interface in org.springframework.data.jpa.domain and inspect how its toPredicate method is used with CriteriaQuery and Subquery. Determine whether the API can support both query types without duplicating specification logic, while preserving existing usage; the issue does not name specific tests or files beyond the interface and package.