no more internal server error if non-logged in users try to log out

shiftregister/app/views.py

@@ -39,7 +39,8 @@ def login(request, token):
     return redirect('index')
 
 def logout(request):
-    del request.session['token']
+    if request.session.get('token'):
+        del request.session['token']
     return redirect('index')
 
 def register(request):