Getting merge request approvers not returning groups.

GET http://domain/api/v3/projects/1/merge_requests/4/approvals

{
	"id": 4,
	"iid": 3,
	"project_id": 1,
	"title": "MR1",
	"description": "",
	"state": "opened",
	"created_at": "2018-05-16T19:51:14.171Z",
	"updated_at": "2018-05-17T18:57:52.165Z",
	"merge_status": "can_be_merged",
	"approvals_required": 1000,
	"approvals_left": 1,
	"approved_by": [
		{
			"user": {
				"id": 4,
				"name": "Test User3",
				"username": "user3",
				"state": "active",
				"avatar_url": "https://www.gravatar.com/avatar/6c4aceaa06ef85f3ae0715b6c70960d7?s=80&d=identicon",
				"web_url": "http://domain/user3"
			}
		},
		{
			"user": {
				"id": 3,
				"name": "Test User2",
				"username": "user2",
				"state": "active",
				"avatar_url": "https://www.gravatar.com/avatar/780a0f7d8632b75d5bce11b4b0e37440?s=80&d=identicon",
				"web_url": "http://domain/user2"
			}
		}
	],
	"suggested_approvers": [],
	"user_has_approved": false,
	"user_can_approve": false
}

PUT http://domain/api/v3/projects/1/merge_requests/3/approvers

Request:
{
	"approver_ids": [3,4],
	"approver_group_ids": [2]
}

Response:
{
	"id": 4,
	"iid": 3,
	"project_id": 1,
	"title": "MR1",
	"description": "",
	"state": "opened",
	"created_at": "2018-05-16T19:51:14.171Z",
	"updated_at": "2018-05-17T18:57:52.165Z",
	"merge_status": "can_be_merged",
	"approvals_required": 1000,
	"approvals_left": 1,
	"approved_by": [
		{
			"user": {
				"id": 4,
				"name": "Test User3",
				"username": "user3",
				"state": "active",
				"avatar_url": "https://www.gravatar.com/avatar/6c4aceaa06ef85f3ae0715b6c70960d7?s=80&d=identicon",
				"web_url": "http://domain/user3"
			}
		},
		{
			"user": {
				"id": 3,
				"name": "Test User2",
				"username": "user2",
				"state": "active",
				"avatar_url": "https://www.gravatar.com/avatar/780a0f7d8632b75d5bce11b4b0e37440?s=80&d=identicon",
				"web_url": "http://domain/user2"
			}
		}
	],
	"suggested_approvers": [],
	"approvers": [
		{
			"user": {
				"id": 4,
				"name": "Test User3",
				"username": "user3",
				"state": "active",
				"avatar_url": "https://www.gravatar.com/avatar/6c4aceaa06ef85f3ae0715b6c70960d7?s=80&d=identicon",
				"web_url": "http://domain/user3"
			}
		},
		{
			"user": {
				"id": 3,
				"name": "Test User2",
				"username": "user2",
				"state": "active",
				"avatar_url": "https://www.gravatar.com/avatar/780a0f7d8632b75d5bce11b4b0e37440?s=80&d=identicon",
				"web_url": "http://domain/user2"
			}
		}
	],
	"approver_groups": [
		{
			"group": {
				"id": 2,
				"name": "test-group",
				"path": "test-group",
				"description": "",
				"visibility": "public",
				"lfs_enabled": true,
				"avatar_url": null,
				"web_url": "http://domain/groups/test-group",
				"request_access_enabled": false,
				"full_name": "test-group",
				"full_path": "test-group",
				"parent_id": null,
				"ldap_cn": null,
				"ldap_access": null
			}
		}
	],
	"user_has_approved": false,
	"user_can_approve": false
}

GET /version

{
    "version": "10.7.3-ee",
    "revision": "584a495"
}

NOTE: I know the GET/PUT urls are different, see #6074 (closed)

Is there another api call that I am expected to do to get the approval groups?