Steps to reproduce:
- Go to any deleted page (e.g., the test case in my userspace). Your account will require admin permissions.
- Use the "diff" link next to an edit to attempt to review a deleted diff.
- The diff would be displayed.
- An error message is displayed ("[Xd8h4ApAME4AAICCybsAAABT] 2019-11-28 01:24:48: Fatal exception of type "InvalidArgumentException").
As suggested here, I have tested with the "safemode=1" argument appended to the URL to rule out an issue with user scripts. This did not change the behavior and the error still occurred. I have tested in Firefox 70.0.1 and Chrome 78.0.3904.108 and the same issue occurs in both browsers.