Missing user name in notification

Description

Steps to reproduce:
The issue happens to built-in content in Alloy sample site.

1. User Alfred logs into the system.
2. Go to Edit View -> View a built-in content such as Alloy Plan page.
3. Show the comments pane.
4. Add a comment to "Created by installer" activity.
5. Tag @Ida user to comment and post.
6. Add another comment to the "Created by installer" activity.
7. Ida logs in and views the notification list.

Expected:
To built-in content that was created by installer, we should show a name standing for installer instead of an empty name.

Actual:
Missing user name in the latest notification: "Alfred commented on 's action Created"