diff --git a/lms/djangoapps/discussion/notifier_api/tests.py b/lms/djangoapps/discussion/notifier_api/tests.py
index 6726cbe681..be1dca8d89 100644
--- a/lms/djangoapps/discussion/notifier_api/tests.py
+++ b/lms/djangoapps/discussion/notifier_api/tests.py
@@ -159,7 +159,7 @@ class NotifierUsersViewSetTest(UrlResetMixin, ModuleStoreTestCase):
         )
         return self.list_view(request)
 
-    def _get_list(self, page=1, page_size=None):
+    def _get_list(self, page=1, page_size=''):
         response = self._make_list_request(page, page_size)
         self.assertEqual(response.status_code, 200)
         self.assertEqual(