Update MergeRequest API state_event option documentation

doc/api/merge_requests.md

@@ -369,17 +369,18 @@ PUT /projects/:id/merge_requests/:merge_request_id
 | --------- | ---- | -------- | ----------- |
 | `id`            | string  | yes | The ID of a project |
 | `merge_request_id` | integer  | yes | The ID of a merge request |
-| `source_branch` | string  | yes | The source branch |
-| `target_branch` | string  | yes | The target branch |
-| `title`         | string  | yes | Title of MR |
+| `target_branch` | string  | no | The target branch |
+| `title`         | string  | no | Title of MR |
 | `assignee_id`   | integer | no  | Assignee user ID |
 | `description`   | string  | no  | Description of MR |
-| `target_project_id` | integer  | no | The target project (numeric id) |
+| `state_event` | string  | no | New state (close/reopen) |
 | `labels` | string  | no | Labels for MR as a comma-separated list |
 | `milestone_id` | integer  | no | The ID of a milestone |
 | `remove_source_branch` | boolean  | no | Flag indicating if a merge request should remove the source branch when merging |
 | `squash` | boolean| no | Squash commits into a single commit when merging |
 
+Must include at least one non-required attribute from above.
+
 ```json
 {
   "id": 1,

lib/api/merge_requests.rb

@@ -140,7 +140,7 @@ module API
       params do
         optional :title, type: String, allow_blank: false, desc: 'The title of the merge request'
         optional :target_branch, type: String, allow_blank: false, desc: 'The target branch'
-        optional :state_event, type: String, values: %w[close reopen merge],
+        optional :state_event, type: String, values: %w[close reopen],
                                desc: 'Status of the merge request'
         use :optional_params
         at_least_one_of :title, :target_branch, :description, :assignee_id,