Cannot edit content item sent for review when user is deleted.

Steps:

1. Create a new user with editor's privileges* or use existing one (* - used User/login & Content/All functions).
2. Log in as this user.
3. Send a content item for review using flex workflow.
4. Log in as admin.
5. Delete the user from step 1 (send to trash and remove from trash).
6. Try to edit the draft created in step 3 (e.g. open it from the View Notifications menu).

Expected: Draft should be possible to edit despite user being deleted.
Actual: Error 500 occurs with exception "An exception has been thrown during the rendering of a template ("Could not find 'Content' with identifier 'array ( 'id' => 59, 'languages' => NULL, 'versionNo' => NULL, )'"). [in vendor/ezsystems/ezplatform-admin-ui/src/bundle/Resources/views/content/content_edit/content_edit.html.twig:74]".

Remarks: On v2.4.2 the problem does not occur when user is deleted via Trash but it does when user is deleted immediately (available from user view mode).

Note:
The issue comes from null value retrieved from ApprovalTimeline.php.