Index: trunk/src/org/openstreetmap/josm/actions/downloadtasks/DownloadOsmChangeTask.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/downloadtasks/DownloadOsmChangeTask.java	(revision 4660)
+++ trunk/src/org/openstreetmap/josm/actions/downloadtasks/DownloadOsmChangeTask.java	(revision 4661)
@@ -63,4 +63,6 @@
         protected void finish() {
             super.finish();
+            if (isFailed() || isCanceled() || downloadedData == null)
+                return; // user canceled download or error occurred
             progressMonitor.subTask(tr("Updating data"));
             UpdatePrimitivesTask task = new UpdatePrimitivesTask(targetLayer, downloadedData.allPrimitives());