在对象id数组中查找对象id使用Mongoose返回空数组

I have two Mongoose schemas:

我有两个蒙古模式:

var EmployeeSchema = new Schema({
    name: String,
    servicesProvided: [{
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Service'
    }]
});

var ServiceSchema = new Schema({
    name: String
});
var