Fix query error

lms/djangoapps/open_ended_grading/open_ended_notifications.py

@@ -66,9 +66,14 @@ def combined_notifications(course, user):
     course_id = course.id
 
     min_time_to_query = user.last_login
-    last_module_seen = StudentModule.objects.filter(student=user, course_id = course_id, modified__gt=min_time_to_query).values('modified').order_by('-modified')[0]
+    last_module_seen = StudentModule.objects.filter(student=user, course_id = course_id, modified__gt=min_time_to_query).values('modified').order_by('-modified')
+    last_module_seen_count = last_module_seen.count()
+
+    if last_module_seen_count>0:
+        last_time_viewed = last_module_seen[0]['modified']
+    else:
+        last_time_viewed = user.last_login
 
-    last_time_viewed = last_module_seen['modified']
     pending_grading= False
 
     img_path= ""