How to access multi-level variable in UEL?

Flowable Engine
1

Given following UEL expression in a sequence flow:

                <![CDATA[${!userService.isSameUser(user.id, user.dept.id)}]]>

I noticed that first level (or root) properties are accessible in the userService bean but user.dept object is converted to string and I’m wondering how to access this and possibly other sub-level objects in the UEL.