Debug time limit handling

ref-test/app/admin/views.py

@@ -291,7 +291,7 @@ def _create_test():
         new_test.start_date = datetime.strptime(new_test.start_date, '%Y-%m-%dT%H:%M')
         new_test.end_date = request.form.get('expiry_date')
         new_test.end_date = datetime.strptime(new_test.end_date, '%Y-%m-%dT%H:%M')
-        new_test.time_limit = request.form.get('time_limit')
+        new_test.time_limit = None if request.form.get('time_limit') == 'none' else int(request.form.get('time_limit'))
         dataset = request.form.get('dataset')
         new_test.dataset = Dataset.query.filter_by(id=dataset).first()
         success, message = new_test.create()