[logback-user] Evaluator and Layout Pattern

[ekkehard]

 If I'm using an evaluator "HAS_MARKER"
which evaluates the Expression
    marker != null

and then in my layout - I'm using this Pattern

-[%marker{HAS_MARKER}]-

it prints
-[]-
 
is there a way to use this Evaluator that nothing is printed ?

thx

ekke