Node.js Mongoose检索my document内部数组的null

我有一个集合，其中一个字段是字符串数组。但是当我使用

find（）

进行查询时，它返回

null

，而在MongoDB指南针中我可以看到它

这是我的文件：

{
   "_id":"5d4894f23f86a41b84303795",
   "position":1,
   "garmentTitle":"My first Garment",
   "garmentURL":"www.firstgarment.com",
   "garmentPictureURL":"/images/first.png",
   "brand":"5d49e60e4eface2a00ac58d7",
   "garmentMaker":"5d49e8854eface2a00ac58d9",
   "garmentPurpose":"5d49e8754eface2a00ac58d8",
   "gender":"5d37546f2f8c280adc60b3fe",
   "garmentCategory":"5d3a4c7f447a7a3afc71a746",
   "fabricComposition":null,
   "garmentSizes":["5d4d211f0fe9591facb9a268"] // <<== This is mentioned array
 }

这是我的控制器：

module.exports.getOneGarmentDataByID = function (req, res) {
    GD.find({_id:req.params.id})
        .exec()
        .then(result => {
            res.status(200).json(result);
        })
        .catch(err => {
            console.log(err);
            res.status(500).json({error:err});
        });
}

请求的路线：

http://localhost:3000/gar/getonegarmentdatabyid/5d4894f23f86a41b84303795

最终结果是：

[
    {
        "garmentSizes": null, <<== returns null!!!
        "_id": "5d4894f23f86a41b84303795",
        "position": 1,
        "garmentTitle": "My first Garment",
        "garmentURL": "www.firstgarment.com",
        "garmentPictureURL": "/images/first.png",
        "brand": "5d49e60e4eface2a00ac58d7",
        "garmentMaker": "5d49e8854eface2a00ac58d9",
        "garmentPurpose": "5d49e8754eface2a00ac58d8",
        "gender": "5d37546f2f8c280adc60b3fe",
        "garmentCategory": "5d3a4c7f447a7a3afc71a746",
        "__v": 0,
        "fabricComposition": null
    }
]

[
{
“garmentSizes”：null，架构类型错误。应为：

garmentSizes: {
    type: [
      {
         type: mongoose.Schema.Types.ObjectId,
         ref: 'GS'
      }
    ],
    required: false
  }

garmentSizes: {
    type: [
      {
         type: mongoose.Schema.Types.ObjectId,
         ref: 'GS'
      }
    ],
    required: false
  }