CastError: Cast to ObjectId failed for value "cover.css"

Question

I try to save a new data in my mongoDB with NodeJS and express. Cover.css comes from Bootstrap. I found a solution by adding _Id in my Schema, but I need to let mongo make _Ids. I can't understand this error. Normally , if I doesnt mention an _Id on my schema, mongoose will create one. But in this error, it seems like I have to send an Id manually. I don't know why Here is it

CastError: Cast to ObjectId failed for value "cover.css" at path "_id" for model "ProductModel"
 messageFormat: undefined,
  stringValue: '"cover.css"',
  kind: 'ObjectId',
  value: 'cover.css',
  path: '_id',
  reason: Error: Argument passed in must be a single String of 12 bytes or a string of 24 hex characters

And my code :

const express = require('express')
var ProductModel = require('./../models/article')
const router = express.Router()

router.get('/new', (req, res) => {
    res.render('products/new', { product: new ProductModel() })
})
router.get('/:id/', async (req, res) => {
    var product = await ProductModel.findById(req.params.id)
    res.render('products/show', { article: product })
router.post('/', async(req, res) => {
    let product = new ProductModel({
        
        Type: req.body.Type,
        Boitier: req.body.Boitier,
        Marque: req.body.Marque,
        Modele: req.body.Modele,
        Annee: req.body.Annee,
        Poids: req.body.Poids,
        Capteur: req.body.Capteur,
        Resolution: req.body.Resolution,
        ISO: { min: req.body.min, max: req.body.max },
        Dimensions: { Hauteur: req.body.Hauteur, Longueur: req.body.Longueur, Profondeur: req.body.Profondeur },
        Charge: req.body.Charge,
        Monture: req.body.Monture,
        Connectique: { USB: req.body.USB, HDMI: req.body.HDMI, mic: req.body.mic, priseCourant: req.body.priseCourant },
        Puissance: req.body.Puissance,
        Temperature: req.body.Temperature,
        Lampe: req.body.Lampe,
        Focale: req.body.Focale
    })
    try {
       product = await product.save()
        res.redirect(`/products/${product.id}/`) 
    } catch (e) {
        res.render('/products/new', { article: product })
        res.send('HUM... embarrassant')
        console.log(e)
    }
    
})

Answer 1

ok. the solution is just to use href="/cover.css" in template link. question is now resolved