Populate subdocument mongoose

I have a Person and Video model.
Person had subdoc with social profils.
According https://mongoosejs.com/docs/populate.html
I want when Video quering populate with ref id.

But I get author: null

let loginProfileSchema = new Schema({ social: String, name: String});
let personschema = new Schema({ ip: [String], user: [loginProfileSchema], videos: { type: Schema.Types.ObjectId, ref: 'Video' }});

 global.Video = mongoose.model('Video', new Schema({author: { type: Schema.Types.ObjectId, ref: 'videoappperson' },urlImage: String, visitorsIp: [String],  videoName: String}

creating of person  let newchild = { _id: new mongoose.Types.ObjectId(),   social: 'github', name: req.user.username}
const newdoc = new Person({ip: req.ip, user: newchild });

 newdoc.save().then(() => console.log('new Person save' + newdoc));

the VIdeo is saved
 const newdoc = new Video({author:mongoose.Types.ObjectId(User_id),videoName: videoName, urlVideo: urlVideo, urlImage:urlImage})

and query
        function (err, docs) {
          if (err) errorhandler(err);

          if (docs) {

               */    res.render('grid', { v: docs,  acBtn: 'allvideo' });