structural search for fields of certain type in class hierarchy

Hi,

I'm trying to use structural search to find all fields that are some sort of Collection in all subclasses of Base.

So given:

class Foo extends Base {
   List list;
}

class Bar extends Foo {
   Set set;
}

I want both these fields to be returned from the search.

I've tried:
class $Class$ {
  $FieldType$ $FieldName$
}

where: $Class$ is set to Base and 'Apply constraint within type hierarchy' is checked. $FieldType$ is set to Collection and 'Apply constraint within type hierarchy' is checked. $FieldName$ is set to nothing and 'This variable is target of the search' is checked.

Nothing is returned.

Regards,
Ittay