Mongodb：不支持从数组到 objectId 的转换

问：

我使用$lookup加入连接。 在正常情况下没有问题。但是使用流水线后，程序给出了一个错误："Unsupported conversion from array to objectId in $convert with no onError value"

{
   $lookup:
          {
            from: "reserves",
            localField: "reserve",
            foreignField: "_id",
            as: "reserve",
          }
}

此代码有效

和结果

{
    "status": "success",
    "message": "okkkk",
    "results": 1,
    "data": [
        {
            "_id": "sdfgsd56",
            "customer": "fghdfbv",
            "price": 170000,
            "off": 30000,

            "reserve": [
                {
                    "_id": "65421d801c128f2ed899a7a4",
                    "customer": "6540debf6ca6663eb886eb46",
                    "service": "65421c961c128f2ed899a631",
                    "__v": 0
                }
            ]
        }
    ]
}

但是由于我们使用管道，我必须更改代码，如下所示，并且出现错误

{
$lookup : {
from:
  "reserves", 'let' : {reserveData : "$reserve"}, as : "reserve", pipeline : [
    {
      $match : {
        $expr : {
          $eq : [ "$_id", {$toObjectId : "$$reserveData"} ],
        }
      },
    },
  ]
}