diff --git a/endpoints/notificationhelper.py b/endpoints/notificationhelper.py
index 66d7ac0dc..37e5bc56b 100644
--- a/endpoints/notificationhelper.py
+++ b/endpoints/notificationhelper.py
@@ -10,7 +10,7 @@ from auth.auth_context import get_authenticated_user, get_validated_oauth_token
 DEFAULT_BATCH_SIZE = 1000
 
 
-def build_event_data(repo, extra_data={}, subpage=None):
+def build_event_data(repo, extra_data=None, subpage=None):
   repo_string = '%s/%s' % (repo.namespace_name, repo.name)
   homepage = '%s://%s/repository/%s' % (app.config['PREFERRED_URL_SCHEME'],
                                         app.config['SERVER_HOSTNAME'],
@@ -30,7 +30,7 @@ def build_event_data(repo, extra_data={}, subpage=None):
     'homepage': homepage,
   }
 
-  event_data.update(extra_data)
+  event_data.update(extra_data or {})
   return event_data
 
 def build_notification_data(notification, event_data, performer_data=None):
@@ -63,14 +63,14 @@ def notification_batch(batch_size=DEFAULT_BATCH_SIZE):
   the callable will be bulk inserted into the queue with the specified batch size.
   """
   with notification_queue.batch_insert(batch_size) as queue_put:
-    def spawn_notification_batch(repo, event_name, extra_data={}, subpage=None, pathargs=[],
+    def spawn_notification_batch(repo, event_name, extra_data=None, subpage=None, pathargs=None,
                                  performer_data=None):
       event_data = build_event_data(repo, extra_data=extra_data, subpage=subpage)
 
       notifications = model.notification.list_repo_notifications(repo.namespace_name,
                                                                  repo.name,
                                                                  event_name=event_name)
-      path = [repo.namespace_name, repo.name, event_name] + pathargs
+      path = [repo.namespace_name, repo.name, event_name] + (pathargs or [])
       for notification in list(notifications):
         notification_data = build_notification_data(notification, event_data, performer_data)
         queue_put(path, json.dumps(notification_data))
@@ -78,7 +78,7 @@ def notification_batch(batch_size=DEFAULT_BATCH_SIZE):
     yield spawn_notification_batch
 
 
-def spawn_notification(repo, event_name, extra_data={}, subpage=None, pathargs=[],
+def spawn_notification(repo, event_name, extra_data=None, subpage=None, pathargs=None,
                        performer_data=None):
   with notification_batch(1) as batch_spawn:
     batch_spawn(repo, event_name, extra_data, subpage, pathargs, performer_data)