"reviewers" config of dependabot causes API error

The reviewers field referenced in the dependabot docs causes an 404 not found API error.

With this example config:

version: 2
updates:
  - package-ecosystem: "bundler"
    directory: "/"
    ...
    assignees:
      - mg
    reviewers:
      - mg

There is a MR correctly created and assigned to MG, but after that an error occurs, probably when dependabot tries to also set the reviewer:

Gitlab::Error::NotFound: Server responded with code 404, message: 404 Not Found. Request URI: https://gitlab.server/api/v4/projects/mg%2Fzammad/merge_requests/8/approvers

Thanks for considering!