ActionView::Template::Error: Hostname not supplied: ''

https://sentry.gitlap.com/gitlab/gitlabcom/issues/41539/

Addressable::URI::InvalidURIError: Hostname not supplied: ''
  lib/gitlab/url_sanitizer.rb:68:in `generate_full_url'
    @full_url.user = credentials[:user]
  lib/gitlab/url_sanitizer.rb:42:in `full_url'
    @full_url ||= generate_full_url.to_s
  app/views/projects/mirrors/_pull.html.haml:28:in `block in _app_views_projects_mirrors__pull_html_haml___2624090915108510646_70001868172500'
    = f.text_field :username_only_import_url, class: 'form-control js-repo-url', placeholder: 'https://username@gitlab.company.com/group/project.git', required: 'required', pattern: "(#{protocols}):\/\/.+", title: 'URL must have protocol present (eg...
  app/views/projects/mirrors/_pull.html.haml:16:in `_app_views_projects_mirrors__pull_html_haml___2624090915108510646_70001868172500'
    = form_for @project, url: project_mirror_path(@project), html: { class: 'gl-show-field-errors project-mirror-push-form js-project-mirror-push-form', autocomplete: 'false', data: { project_mirror_endpoint: ssh_host_keys_project_mirror_path(@project, ...
  app/views/projects/mirrors/_show.html.haml:5:in `_app_views_projects_mirrors__show_html_haml__4573455178690476552_70001868894520'
    = render 'projects/mirrors/pull'
...
(191 additional frame(s) were not displayed)

ActionView::Template::Error: Hostname not supplied: ''

ActionView::Template::Error: Hostname not supplied: ''

/cc @markglenfletcher