[rules-users] How to handle generics in Drools?

Hello, In my rules file I'd like to set something like this: rule "mayThrowDice" when $user : User($gp : gameplay) $gameplay(this == $gp) then exists List<Boost>() { ..... some business logic } end But it looks like there is no generics support. How can I make sure there is a List of type Boost inserted into the session? Thank you, Martin