Index: trunk/src/org/openstreetmap/josm/io/MirroredInputStream.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/MirroredInputStream.java	(revision 3010)
+++ trunk/src/org/openstreetmap/josm/io/MirroredInputStream.java	(revision 3011)
@@ -79,4 +79,6 @@
      */
     public InputStream getZipEntry(String extension, String namepart) {
+        if (file == null)
+            return null;
         InputStream res = null;
         try {