Sometimes merging merge requests using the API fails without producing an error
Sometimes when merging a merge request using the API, the MR won't be merged without producing an error. Instead, the API just responds with the merge request details without including any merge commit details. The Delivery team ran into this in https://gitlab.com/gitlab-org/release-tools/issues/277.
The API does seem to include a merge_error
field on a merge request, and sets this when merging somehow fails. However, when a merge fails this should lead to an HTTP error, instead of the API responding with some OK status. This message should include the merge error, making it much easier to debug why the merge failed.