zone_name attribute is not set in Response body of REST API call for creation of zone transfer request.

When we make REST API call for creation of zone ownership transfer request. The response to API call has zone_id set with zone id but zone name is set to 'null'.

$ curl -g -i -X POST http://192.168.11.182:9001/v2/zones/54926a13-2fb4-41db-bdb2-d344c502be4c/tasks/transfer_requests -H "User-Agent: python-designateclient-2.1.0" -H "Content-Type: application/json" -H "Accept: application/json" -H "X-Auth-Token: 8beeb321c38a467dbc4dc65eb820f258" -d '{"target_project_id": "9cc52dd7649c4aa99fa9db2fb94dabb8"}'

HTTP/1.1 201 Created
Location: http://192.168.11.182:9001/v2/zones/tasks/transfer_requests/9e49da89-9a7c-4878-9d20-b2dd1d327d37
Content-Length: 459
Content-Type: application/json; charset=UTF-8
X-Openstack-Request-Id: req-9ce659dd-23da-419e-8ec7-367a1f995979
Date: Tue, 10 May 2016 02:29:57 GMT

{"status": "ACTIVE", "target_project_id": "9cc52dd7649c4aa99fa9db2fb94dabb8", "zone_id": "54926a13-2fb4-41db-bdb2-d344c502be4c", "links": {"self": "http://192.168.11.182:9001/v2/zones/tasks/transfer_requests/9e49da89-9a7c-4878-9d20-b2dd1d327d37"}, "created_at": "2016-05-10 02:29:57", "updated_at": null, "key": "EQ3M4GNO", "zone_name": null, "project_id": "10457ad1fe074f4a89bb1e4c0cd83d40", "id": "9e49da89-9a7c-4878-9d20-b2dd1d327d37", "description": null}

If we have zone_id set with some zone id then zone_name should also be set with the corresponding zone name.