[rules-users] check if a Enum object is present in condition

Hello, I try to put a condition in my LHS, such as: rule "initial_playground_dialog" #agenda-group "firstTimeUser" #salience 99 when $gst : GameStateController(!hasEventOccurred("initial_playground_dialog")) $list : List() $screen : FrontendScreen.PLAYGROUND then .... end where 'FrontendScreen' is an enum and PLAYGROUND is its property. However I get a syntax error. What's the proper way to check for and assign such a session object? Any help is appreciated! Best regards, Martin