Index: trunk/src/org/openstreetmap/josm/io/session/GenericSessionExporter.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/session/GenericSessionExporter.java	(revision 9752)
+++ trunk/src/org/openstreetmap/josm/io/session/GenericSessionExporter.java	(revision 9753)
@@ -208,5 +208,8 @@
         } else {
             try {
-                file.appendChild(support.createTextNode(layer.getAssociatedFile().toURI().toURL().toString()));
+                File f = layer.getAssociatedFile();
+                if (f != null) {
+                    file.appendChild(support.createTextNode(f.toURI().toURL().toString()));
+                }
             } catch (MalformedURLException e) {
                 throw new IOException(e);