When receiving an email for a build that ran on a branch with a “#” or any other encoding-required character in the name (such as fix#44-blah-blah), the URL does not get escaped and thus leads to a 404 error.
Example:
If a build email was received about the branch fix#44-blah-blah on the repository https://github.com/me/myproject, it would be formatted https://github.com/me/myproject/tree/fix#44-blah-blah.
It should be formatted https://github.com/me/myproject/tree/fix%2344-blah-blah instead, to avoid a 404 error from GitHub.