Merge branch 'docs/api-nil' into 'master'

Document how to remove assignees, labels, and milestones form the issue and MRs API

See merge request gitlab-org/gitlab-ce!15664

doc/api/issues.md

@@ -514,9 +514,9 @@ PUT /projects/:id/issues/:issue_iid
 | `title`        | string  | no       | The title of an issue                                                                                      |
 | `description`  | string  | no       | The description of an issue                                                                                |
 | `confidential` | boolean | no       | Updates an issue to be confidential                                                                        |
-| `assignee_ids`  | Array[integer] | no       | The ID of the users to assign the issue to                                                                    |
-| `milestone_id` | integer | no       | The ID of a milestone to assign the issue to                                                               |
-| `labels`       | string  | no       | Comma-separated label names for an issue                                                                   |
+| `assignee_ids`  | Array[integer] | no  | The ID of the user(s) to assign the issue to. Set to `0` or provide an empty value to unassign all assignees.  |
+| `milestone_id` | integer | no       | The ID of a milestone to assign the issue to. Set to `0` or provide an empty value to unassign a milestone.|
+| `labels`       | string  | no       | Comma-separated label names for an issue. Set to an empty string to unassign all labels.                   |
 | `state_event`  | string  | no       | The state event of an issue. Set `close` to close the issue and `reopen` to reopen it                      |
 | `updated_at`   | string  | no       | Date time string, ISO 8601 formatted, e.g. `2016-03-11T03:45:40Z` (requires admin or project owner rights) |
 | `due_date`     | string  | no       | Date time string in the format YEAR-MONTH-DAY, e.g. `2016-03-11`                                           |

doc/api/merge_requests.md

@@ -528,11 +528,11 @@ PUT /projects/:id/merge_requests/:merge_request_iid
 | `merge_request_iid`    | integer | yes      | The ID of a merge request                                                       |
 | `target_branch`        | string  | no       | The target branch                                                               |
 | `title`                | string  | no       | Title of MR                                                                     |
-| `assignee_id`          | integer | no       | Assignee user ID                                                                |
+| `assignee_id`          | integer | no       | The ID of the user to assign the merge request to. Set to `0` or provide an empty value to unassign all assignees.  |
+| `milestone_id`         | integer | no       | The ID of a milestone to assign the merge request to. Set to `0` or provide an empty value to unassign a milestone.|
+| `labels`               | string  | no       | Comma-separated label names for an merge request. Set to an empty string to unassign all labels.                   |
 | `description`          | string  | no       | Description of MR                                                               |
 | `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 |
 | `discussion_locked`    | boolean | no       | Flag indicating if the merge request's discussion is locked. If the discussion is locked only project members can add, edit or resolve comments. |