Index: /applications/editors/josm/plugins/wikipedia/src/org/wikipedia/WikipediaToggleDialog.java
===================================================================
--- /applications/editors/josm/plugins/wikipedia/src/org/wikipedia/WikipediaToggleDialog.java	(revision 28473)
+++ /applications/editors/josm/plugins/wikipedia/src/org/wikipedia/WikipediaToggleDialog.java	(revision 28474)
@@ -319,4 +319,7 @@
                         Main.parent,
                         tr("Enter the Wikipedia category"));
+                if (category == null) {
+                    return;
+                }
                 final String url = "http://toolserver.org/~daniel/WikiSense/CategoryIntersect.php?"
                         + "wikilang=" + wikipediaLang.get()