middleware file forgot to include

lms/djangoapps/django_comment_client/middleware.py

+from comment_client import CommentClientError
+from django_comment_client.utils import JsonError
+import json
+
+class AjaxExceptionMiddleware(object): 
+    def process_exception(self, request, exception):
+        if isinstance(exception, CommentClientError) and request.is_ajax():
+            return JsonError(json.loads(exception.message))
+        return None