Message boards show empty value for thread replies of deleted users

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X, Master
• Fix Version/s: 7.0.0 DXP FP84, 7.0.10.12 DXP SP12, 7.0.X, 7.1.10 DXP FP12, 7.1.X, 7.2.X, Master
• Component/s: Message Boards
• Labels:
  • 7.2-won't
  • SMEQAFP3
  • ee-ts
  • liferay-fixpack-de-84-7010
  • liferay-fixpack-dxp-12-7110
• Branch Version/s:
  7.1.x, 7.0.x
• Backported to Branch:
  Committed
• Story Points: 0.25
• Fix Priority: 3
• Sprint: 026 - Raichu
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/73469

Steps to reproduce:

1. Create user A and add it to the default Liferay site.
2. Create user B and add it to the default Liferay site.
3. Place a Message Boards portlet on the welcome page.
4. Sign in with A and create a thread "thread one".
5. Sign in with B and create a thread "thread two".
6. As user B, reply to thread one.
Checkpoint: For thread two, you can see "User B, modified x minutes ago". For thread one, you can see "User B replied x minutes ago"
7. As portal administrator, deactivate and delete user B.
8. Look at the Message Board portlet (either as admin or user A)

Result: For thread two, you can see "User B, modified x minutes ago" (so you can still see user B's name). But for thread one, you see "replied x minutes ago": user B's name is replace with an empty string.
Expected: For thread one you should see "User B replied x minutes ago".