Index: src/org/openstreetmap/josm/plugins/validator/tests/DuplicateWay.java
===================================================================
--- src/org/openstreetmap/josm/plugins/validator/tests/DuplicateWay.java	(revision 22711)
+++ src/org/openstreetmap/josm/plugins/validator/tests/DuplicateWay.java	(working copy)
@@ -166,8 +166,7 @@
         //Note: nodes are not deleted, these can be detected and deleted at next pass
         ways.remove(wayToKeep);
         commands.add(new DeleteCommand(ways));
-        Main.main.undoRedo.add(new SequenceCommand(tr("Delete duplicate ways"), commands));
-        return null;
+        return new SequenceCommand(tr("Delete duplicate ways"), commands);
     }
 
     @Override