marge-bot: 404 on MR with gitlab 12.5

As soon as I updated my gitlab to 12.5, marge-bot broke with:

Traceback (most recent call last):
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/bin/.marge.app-wrapped", line 4, in <module>
    marge.app.main()
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/app.py", line 314, in main
    marge_bot.start()
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/bot.py", line 42, in start
    self._run(repo_manager)
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/bot.py", line 60, in _run
    projects,
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/bot.py", line 98, in _process_projects
    self._process_merge_requests(repo_manager, project, merge_requests)
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/bot.py", line 175, in _process_merge_requests
    merge_job.execute()
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/single_merge_job.py", line 23, in execute
    approvals = merge_request.fetch_approvals()
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/merge_request.py", line 190, in fetch_approvals
    approvals.refetch_info()
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/approvals.py", line 18, in refetch_info
    self._info = self._api.call(GET(approver_url))
  File "/nix/store/q1p3m25nflp834hiwfy7cxxwfpqvcyjq-python3.6-marge-0.9.1/lib/python3.6/site-packages/marge/gitlab.py", line 65, in call
    raise error(response.status_code, err_message)
marge.gitlab.NotFound: (404, {'error': '404 Not Found'})

and this message on the MR comments: I'm broken on the inside, please somebody fix me... 😢