ArgumentError: wrong number of arguments (given 1, expected 2)

https://sentry.gitlab.net/gitlab/gitlabcom/issues/1186398/

ArgumentError: wrong number of arguments (given 1, expected 2)
  auto_merge/add_to_merge_train_when_pipeline_succeeds_service.rb:27:in `abort'
    def abort(merge_request, reason)
  auto_merge/add_to_merge_train_when_pipeline_succeeds_service.rb:16:in `process'
    return abort(merge_request) unless merge_train_service.available_for?(merge_request)
  auto_merge_service.rb:36:in `process'
    get_service_instance(merge_request.auto_merge_strategy).process(merge_request)
  auto_merge_process_worker.rb:12:in `block in perform'
    .process(merge_request)
  active_support/core_ext/object/try.rb:16:in `try!'
    yield self
...
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wrong number of arguments (given 1, expected 2)