<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=355455) </details> <!--IssueSummary end--> The current behavior of the [Merge Request Accept](https://docs.gitlab.com/ee/api/merge_requests.html#merge-a-merge-request) API is that it yields a `405 METHOD NOT ALLOWED` error in case the `merge_when_pipeline_succeeds` field is `true`, but the pipeline doesn't exist. I kinda understand why that may not be a valid request, however, I think it makes clients considerably easier to implement if the field is gracefully ignored in case the MR branch doesn't run a pipeline. IMHO, the current implementation isn't a measure of "protecting" against accidental merges, because that's what the project configured `Pipeline must succeed` flag is for. Related: #353984