MongooseJS FindById ObjectId

I have this simple schema:

var CategorySchema = new mongoose.Schema({
    name: String,
    description: String
});

I get id as URL parameter:

var id = req.params.id;
Category.findById(id, function(err, blogshop){
...
});

Do I need to use mongoose.Schema.Types.ObjectId; or passing the hex value is ok? Thanks