Index: umc/app.js
===================================================================
--- umc/app.js	(Revision 30914)
+++ umc/app.js	(Arbeitskopie)
@@ -110,8 +110,10 @@
 
 	onLogin: function(username) {
 		// save the username internally and as cookie
-		dojo.cookie('UMCUsername', username, { expires: 100, path: '/' });
-		umc.tools.status('username', username);
+		if (username !== undefined) {
+			dojo.cookie('UMCUsername', username, { expires: 100, path: '/' });
+			umc.tools.status('username', username);
+		}
 
 		// set the UCR session timeout value
 		umc.tools.ucr('umc/http/session/timeout').then( function(res) {