Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java	(revision 17796)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java	(revision 17797)
@@ -186,5 +186,5 @@
         FACTORY_MAP.put("is_anticlockwise", Factory.ofEnv(Functions::is_anticlockwise));
         FACTORY_MAP.put("is_clockwise", Factory.ofEnv(Functions::is_clockwise));
-        FACTORY_MAP.put("is_prop_set", Factory.ofEnv(String.class, Functions::is_prop_set));
+        FACTORY_MAP.put("is_prop_set", Factory.ofEnv(String.class, String.class, Functions::is_prop_set, Functions::is_prop_set));
         FACTORY_MAP.put("is_right_hand_traffic", Factory.ofEnv(Functions::is_right_hand_traffic));
         FACTORY_MAP.put("is_similar", Factory.of(String.class, String.class, Functions::is_similar));