Repository mirroring url leads to blank page

After setting up the repository mirroring, the url is shown on the project page.

I've done this for my fork of the GitLab CE repo. My project page looks like in the screenshot.

Problem: the url leads to a blank page.

Either

remove the link or
redirect urls such as https://gitlab.com/gitlab-org/gitlab-ce.git to https://gitlab.com/gitlab-org/gitlab-ce