Making a request for a download of a page without an attached file causes NPE

STEPS TO REPRODUCE
1. Run a XWiki 18.8.0
2. Request the download URL of an existing page without a file name:

http://localhost:8080/xwiki/bin/download/Sandbox/TestPage3

To clarify the expectations:

• when requesting the view of a page, /bin/view/Main/ returns 302 (normal).
• when requesting the download URL of a non-existing attached file, /bin/download/Main/WebHome/nosuchfile.png returns 404 (normal).

EXPECTED RESULTS
The "attachment not found" response (404), or the redirection filter ignores the URL.

ACTUAL RESULTS
Actual: Shown error is

Caused by: java.lang.NullPointerException: Cannot read field "parent" because "reference" is null

and an "Uncaught exception" warning in the log:

plus error 500 in the console: