From 58031587de2dd5d80ac219113911fa78724d35dd Mon Sep 17 00:00:00 2001
From: Sebastian Serth <Sebastian.Serth@hpi.de>
Date: Wed, 4 Mar 2020 17:57:45 +0100
Subject: [PATCH] Check @exercise prior usage

---
 app/controllers/concerns/lti.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/app/controllers/concerns/lti.rb b/app/controllers/concerns/lti.rb
index 6cd3a64a..c8875404 100644
--- a/app/controllers/concerns/lti.rb
+++ b/app/controllers/concerns/lti.rb
@@ -110,7 +110,7 @@ module Lti
                 else
                   proxy_exercise.get_matching_exercise(@current_user)
                 end
-    session[:lti_exercise_id] = @exercise.id
+    session[:lti_exercise_id] = @exercise.id if @exercise
     refuse_lti_launch(message: t('sessions.oauth.invalid_exercise_token')) unless @exercise
   end