Index: trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagCheckerRule.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagCheckerRule.java	(revision 18761)
+++ trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagCheckerRule.java	(revision 18762)
@@ -277,5 +277,5 @@
         } else {
             final Object val = errors.keySet().iterator().next().val;
-            selector = selector == null ? whichSelectorMatchesPrimitive(p) : selector;
+            selector = selector == null && p != null ? whichSelectorMatchesPrimitive(p) : selector;
             return String.valueOf(
                     val instanceof Expression