--- a/client/js/models.js	Sun May 18 10:31:12 2014 +0200
+++ b/client/js/models.js	Sun May 25 13:45:24 2014 +0900
@@ -12,7 +12,12 @@
             var r = Math.random()*16|0, v = c === 'x' ? r : (r&0x3|0x8);
             return v.toString(16);
         });
-        return obj.type + "-" + guid;
+        if(typeof obj !== 'undefined') {
+            return obj.type + "-" + guid;
+        }
+        else {
+            return guid;
+        }
     };