How to use save in Node js?

I'm having a study project using Node JS with MongoDB and I'm having a hard time saving a record in the database, I'm using the method that way.

function postRestaurant (req, res) {
    var restaurants = new Restaurants(req.body);
    restaurants
    .save
    ((err, restStored) => {
        if(err){
            res.status(500).send({message: 'Error do servidor'});
        }else{
            if(!restStored){
                res.status(404).send({message: 'No existe restaurant'});
            }else{
                res.status(200).send({restaurants: restStored});
            }
        }
    });

}

When I submit the method it is falling into error 500, where am I wrong?