Index: trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java	(revision 9858)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/ExpressionFactory.java	(revision 9859)
@@ -1137,5 +1137,5 @@
             });
             final Collection<Float> nonNullList = Utils.filter(floats, Predicates.not(Predicates.isNull()));
-            return computeMax ? Collections.max(nonNullList) : Collections.min(nonNullList);
+            return nonNullList.isEmpty() ? Float.NaN : computeMax ? Collections.max(nonNullList) : Collections.min(nonNullList);
         }