Sharing pane: Failed to construct 'URL'

I am getting the following error message (in html page) when opening the Sharing pane of a newly created folder:

Error reading ACL. status Can't get headers to find ACL for https://: Failed to load https:// Fetcher: fetch failed: TypeError: Failed to construct 'URL': Invalid URL status: 999: ( No ACL pointer https:// Can't get headers to find ACL for https://: Failed to load https:// Fetcher: fetch failed: TypeError: Failed to construct 'URL': Invalid URL status: 999)undefined

The Browser console says:

Failed to load resource: the server responded with a status of 404 ()
fetcher.js:1018 @@ Recording GET failure for <https://angelo.veltens.org/public/test/.acl>: 404
fetcher.js:952 Failed to load  <https://angelo.veltens.org/public/test/.acl> Fetcher: <https://angelo.veltens.org/public/test/.acl> 

This should be fine so far, since I do not have a dedicated .acl file in that folder. But then:

fetcher.js:871 Fetcher: <https://> Non-HTTP fetch error: TypeError: Failed to construct 'URL': Invalid URL
fetcher.js:1018 @@ Recording GET failure for <https://>: 999
fetcher.js:952 Failed to load  <https://> Fetcher: fetch failed: TypeError: Failed to construct 'URL': Invalid URL

Start in fetcher.js around lines 871, 952, and 1018, then reproduce the Sharing pane request sequence for a newly created folder without a .acl file. Trace how the 404 response is handled before the invalid URL is fetched; done means the pane no longer attempts a request with an empty or invalid URL.