The origins we have imported from Google Code end with a slash.
For instance: https://archive.softwareheritage.org/api/1/origin/hg/url/https://atlasmapper.googlecode.com/hg/
Some of the browse URLs succeed, e.g. https://archive.softwareheritage.org/browse/origin/hg/url/https://atlasmapper.googlecode.com/hg//, but only with a double slash at the end. Trying to go further fails with a None-related error.
We should review all navigation paths containing origin URLs to make sure they work with URLs ending with a slash.