As all my requests are working fine, I have a problem with the put. req.body stays empty and then gives that error :

errmsg: "'$set' is empty. You must specify a field like so: {$set: {: ...}}"

PUT :

router.put('/books/:name', (req, res, next) => {
    const localdb = db.client.db(process.env.DB_NAME);
    const collection = localdb.collection(process.env.COLL_BOOKS);
    collection.replaceOne(
        { "name": req.params.name },
        { $set: req.body },
        function (err) {
            if (err) throw err
            res.status(201).send(true);

        });

App.js

const express = require('express'),
    app = express();
os = require('os');
const bodyParser = require('body-parser');
const cors = require('cors');
const router = require('./router.js')
require('dotenv').config()


app.use(cors());
app.use(bodyParser.json());

app.use('/api/v1', router);

const port = (process.env.PORT || '3001');

let server = app.listen(port, os.hostname(), () => {
    let host = server.address().address,
        port = server.address().port;
    console.log("Example app listening at ", host, port);
});

axios request :

 updateItem = newBook => {
        Axios.put(process.env.REACT_APP_API_PATH_BOOKS + `${newBook.name}`, newBook)
            .then(res => {
                this.setState({ newBook: res.data });
                this.props.history.push('/admin');
            })
            .catch(err => console.log(err));
    }

I don't understand what I am doing wrong