Index: src/org/openstreetmap/josm/gui/mappaint/mapcss/Selector.java
===================================================================
--- src/org/openstreetmap/josm/gui/mappaint/mapcss/Selector.java	(revision 15918)
+++ src/org/openstreetmap/josm/gui/mappaint/mapcss/Selector.java	(working copy)
@@ -439,7 +439,8 @@
                 if (right instanceof OptimizedGeneralSelector
                         && ((OptimizedGeneralSelector) right).matchesBase(OsmPrimitiveType.WAY)) {
                     final CrossingFinder crossingFinder = new CrossingFinder(e);
-                    crossingFinder.visit(e.osm.getDataSet().searchWays(e.osm.getBBox()));
+                    if (e.osm.getDataSet() != null)
+                        crossingFinder.visit(e.osm.getDataSet().searchWays(e.osm.getBBox()));
                 }
                 return e.children != null;
             } else if (ChildOrParentSelectorType.SIBLING == type) {