Using JPA2 criteria API without Metamodel on a List property

How can I formulate the following JPA2 criteria query without using the metamodel classes:

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Employee> cq = cb.createQuery(Employee.class);
Root<Employee> emp = cq.from(Employee.class);
cq.where(cb.isEmpty(emp.get(Employee_.projects)));
cq.select(emp);

I would like to use:

cq.where(cb.isEmpty(emp.get("projects")));

But I cant figure out how to convert the Path to an Expression, which is needed by cb.isEmpty...

Thanks.