--- a/progs/ap3.js	Tue Sep 26 12:03:24 2017 +0100
+++ b/progs/ap3.js	Tue Sep 26 12:10:41 2017 +0100
@@ -15,8 +15,7 @@
 }
 
 app.get('/', function(req, res){
-    var counter = gt_cookie(req.cookies.counter) || 0;
+    var counter = gt_cookie(req.cookies.counter || "") || 0;
     res.cookie('counter', mk_cookie(counter + 1));
     ...
 });
-