{
  "fields": [
    {
      "facet": false,
      "index": true,
      "infix": false,
      "locale": "",
      "name": "productId",
      "optional": true,
      "sort": false,
      "type": "string",
      "reference": "products._id"
    }
  ]
}

{
  "message": "There are duplicate field names in the schema."
}