fix bug for empty objects

courses/reports/views.py

@@ -361,12 +361,18 @@ class UserAccessView(views.APIView):
 
         last_login = ''
         last_access = ''
+        last_completed_activity = ''
         accesses_7_days = 0
         accesses_30_days = 0
 
         if actions:
-            last_access = self.format_date(actions.filter(verb='access').last().timestamp)
-            last_completed_activity = self.format_date(actions.filter(verb='answered').order_by('timestamp').last().timestamp)
+            last_access_obj = actions.filter(verb='access').last()
+            last_activity_obj = actions.filter(verb='answered').last()
+
+            if last_access_obj:
+                last_access = self.format_date(last_access_obj.timestamp)
+            if last_activity_obj:
+                last_completed_activity = self.format_date(last_completed_activity_obj.timestamp)
             last_login = self.format_date(user.last_login)
 
             time_delta = timezone.now() - timedelta(days=7)