URL normalization is defined and it doesn't include collapsing slashes.

Not that you can include custom normalization rules (like collapsing slashes, tolower()ing the entire path, removing the query part of the URL), but that's not part of the standard. If you're doing anything extra, the risk of breaking stuff is on you.

If someone gives you a nonsense URL, the correct response is 404, not to try and guess what they could've maybe meant.