FIX: Fix NotificationSerializer.

FIX: Fix NotificationSerializer.

diff --git a/plugin.rb b/plugin.rb
index 2278a76..0fee16d 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -317,7 +317,7 @@ after_initialize do
   end
 
   add_to_serializer(:notification, :include_topic_key?) do
-    scope&.user.present? && object.topic.private_message?
+    scope&.user.present? && object&.topic&.private_message?
   end
 
   # +topic_id+ and +raws+

GitHub sha: cd0837be