[Medium] nested specifications problem

NestedSpecificationProblem.cs

public sealed class ActiveDepartmentSpecification : LinqSpecification<Department>
{
    public override Expression<Func<Department, bool>> AsExpression() => x => x.Active;
}

public sealed class UserWithActiveDepartmentSpecification : LinqSpecification<User>
{
    // see, we can't reuse ActiveDepartmentSpecification here:
    public override Expression<Func<User, bool>> AsExpression() => x => x.Departments.Any(z => z.Active);
}