You can't call post.person when post is nil. We should probably just reject and delete the invalid notifications in the controller, keeping them in the view is aggravating

app/helpers/notifications_helper.rb

@@ -25,7 +25,7 @@ module NotificationsHelper
       if post
         "#{translation(target_type, post.person.name)} #{link_to t('notifications.post'), object_path(post)}".html_safe
       else
-        "#{translation(target_type, post.person.name)} #{t('notifications.deleted')} #{t('notifications.post')}"
+        t('notifications.also_commented_deleted')
       end
     else
     end

config/locales/diaspora/en.yml

@@ -227,6 +227,7 @@ en:
       mentioned: "has mentioned you in their"
       post: "post"
       deleted: "deleted"
+      also_commented_deleted: "commented on a deleted post"
       index:
         notifications: "Notifications"
         mark_all_as_read: "Mark All as Read"