Issue with $ref in Swagger 1.2

$ref-issue.json

{
   "swaggerVersion": "1.2",
   "apis": [

      {
         "operations": [

            {
               "parameters": [
                  {
                     "paramType": "path",
                     "required": true,
                     "type": "string",
                     "name": "pk"
                  },
                  {
                     "name": "full_name",
                     "format": "string",
                     "paramType": "form",
                     "required": false,
                     "type": "FullNameSerializer",
                     "description": ""
                  }
               ],
               "nickname": "Subject_partial_update",
               "notes": "",
               "summary": "",
               "type": "SubjectSerializer",
               "method": "PATCH"
            }
         ],
         "path": "/api/subjects/{pk}/",
         "description": ""
      }
   ],
   "models": {
      "FullNameSerializer": {
         "required": [],
         "id": "FullNameSerializer",
         "properties": {
            "name_first": {
               "description": null,
               "required": false,
               "readOnly": false,
               "type": "string"
            }
         }
      },
      "SubjectSerializer": {
         "required": [
            "full_name"
         ],
         "id": "SubjectSerializer",
         "properties": {
            "full_name": {
               "description": null,
               "required": true,
               "readOnly": false,
               "$ref": "FullNameSerializer"
            }
         }
      }
   },
   "basePath": "http://127.0.0.1:8000",
   "resourcePath": "/api",
   "apiVersion": ""
}