POST method does not work properly Node.js and express

Question

good evening, by way of tests I created a small API to understand its functioning, however when running the POST method I found that it only returns me the empty keys:

[
{}
]

The correct thing would be to return me like this: (when I run GET after POST)

  [
    {
        "name": "Leandro",
        "id": "1"
    }
  ]

I thought it could be my code but I took the one from the class to test and got the same result, I tried to give permission to more in the manipulations of the files but it did not solve, if someone knows or who has already been through so all help is welcome, remembering that I am beginner in Node.js:

Follows my code:

index js.

const express = require('express')
const bodyParser = require('body-parser')

const usersRoute = require('./routes/usersRoute')
const port = 3000

const app = express()

app.use(bodyParser.urlencoded({ extended: false }))

usersRoute(app)

app.get('/', (req, res) => res.send('Olá mundo!'))

app.listen(port, () => console.log(`Express rodando na porta ${port}`)) 

usersRoute.js:

const fs = require('fs')
const { join } = require('path')

const filePath = join(__dirname, 'users.json');

const getUsers = () => {
    const data = fs.existsSync(filePath)
        ? fs.readFileSync(filePath)
        : []

    try {
        return JSON.parse(data);
    } catch (e) {
        return [];      
    }
};

const saveUser = (users) => fs.writeFileSync(filePath, JSON.stringify(users, null, '\t'));

const userRouter = (app) => {

    app.route('/users/:id?')
        .get((req, res) => {
            const users = getUsers()
            res.send({ users })
        })
        .post((req, res) => {
            const users = getUsers()

            users.push(req.body)
            saveUser(users)

            res.status(201).send('OK')
        })
        .put((req, res) => {
            const users = getUsers()
            saveUser(users.map(user => {
                if (user.id === req.params.id) {
                    return {
                        ...user,
                        ...req.body
                    }
                }

                return user
            }))

            res.status(200).send('OK')
        })
        .delete((req, res) => {
            const users = getUsers()
            saveUser(users.filter(user => user.id !== req.params.id))

            res.status(200).send('OK')
        })
}

module.exports = userRouter

and the POST method I run with Postman:

localhost:3000/users?name=Lucas&id=1