Why do I get this error? Cast to ObjectId failed

I am working with MongoDB and made this a%% share% correctly with and I get this result:

{
    "ok": true,
    "mensaje": "Petición realizada correctamente",
    "folios": [
        {
            "folioLineas": [
                {
                    "nivelDeUrgencia": "URGENTE",
                    "almacen": true,
                    "_id": "5b6b1ec0b34c1b0e3cc010e9",
                    "folio": "5b6b147ab34c1b0e3cc010e0",
                    "modeloCompleto": {
                        "_id": "5b6b1e79b34c1b0e3cc010e8",
                        "modelo": "5b6b0e6bb34c1b0e3cc010de",
                        "tamano": "5b6b1e5eb34c1b0e3cc010e1",
                        "color": "5b6b1e5eb34c1b0e3cc010e2",
                        "terminado": "5b6b1e5eb34c1b0e3cc010e3",
                        "marcaLaser": "5b6b1e79b34c1b0e3cc010e7",
                        "versionModelo": "5b6b1e5eb34c1b0e3cc010e4",
                        "__v": 0
                    },
                    "cantidad": 18300,
                    "marcaLaser": {
                        "_id": "5b6b1e79b34c1b0e3cc010e7",
                        "marcaLaser": "ESTA ES LA MARCA LASER",
                        "__v": 0
                    },
                    "__v": 0
                }
            ],
}

After I try to popular my GET with this code:

//... Todo el get
.populate({
            path: 'folioLineas',
            populate: {
                path: 'modeloCompleto marcaLaser',
                populate: {
                    path: 'marcaLaser'
                }
            }
        })

//... Más código.

But Mongo returns the following error:

{
    "ok": false,
    "mensaje": "Error cargando folios.",
    "errors": {
        "message": "Cast to ObjectId failed for value \"ESTA ES LA MARCA LASER\" at path \"_id\" for model \"MarcaLaser\"",
        "name": "CastError",
        "stringValue": "\"ESTA ES LA MARCA LASER\"",
        "kind": "ObjectId",
        "value": "ESTA ES LA MARCA LASER",
        "path": "_id"
    }
}

If I remove the last _id the code works, but that last field path: 'marcaLaser' I want it popular. How to avoid this behavior ?, or What could be doing wrong what mongoose tries to fill the field marcaLaser with the text of _id ?

This is the marcaLaser model:

var mongoose = require('mongoose');

var Schema = mongoose.Schema;
var uniqueValidator = require('mongoose-unique-validator');

var marcaLaserSchema = new Schema({

    laser: { type: String, unique: true },
    imagen: { type: String },


    // Esto de aqui es para que mongose no escriba
    //  marcaLasers en vez de marcaLaseres
}, { collection: 'marcasLaser' });

marcaLaserSchema.plugin(uniqueValidator, { message: ' \'{PATH}\' debe ser único.' });
module.exports = mongoose.model('MarcaLaser', marcaLaserSchema);