schema validation fails although parameter is available

I created a REST api and want to validate the body and the params before calling the controller logic. For the validation I use Joi (https://www.npmjs.com/package/joi).

Let's say I have a route with one url parameter and some body variables. The params object contains this url parameter but Joi still returns a 400. The detail message is

"userId" is required

I tried to create a minimalistic example showing my code. To reproduce the error create the app.js file

const express = require('express');
const bodyParser = require('body-parser');
const morgan = require('morgan');
const cors = require('cors');

const app = express();
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(cors());

app.use('/users', require('./routes/users.js'));

app.listen(3000);

Due to the fact each validation fails there is only one route required to test it. Create users.js with the following content

const express = require('express');
const router = express.Router();

const usersController = require('../controllers/users.js');
const usersControllerPolicy = require('../policies/users.js');

router.get('/:userId', usersControllerPolicy.getUserById, usersController.getUserById);

module.exports = router;

And this users.js controller file

exports.getUserById = async (req, res, next) => {
    const { userId } = req.params;
    return res.status(200).json("everything is fine");
};

When it comes to the policy I created the users.js policy which adds the required schema to the middleware

const joi = require('joi');

const schemaValidation = require('../middleware/schemaValidation.js');

module.exports = {
    getUserById: (req, res, next) => {
        schemaValidation({
            params: {
                userId: joi.string().guid().required()
            },
            body: {}
        }, req, res, next);
    }
}

and then the schema gets validated by my schemaValidation.js

const joi = require('joi');

module.exports = (schema, req, res, next) => {
    const { error } = joi.validate(req, schema);

    if (error)
        return res.status(400).json("something went wrong");

    next(); // execute the controller logic
}

As you can see I pass in the whole req object. I do this because sometimes I have to validate the body and the params. The url parameter userId is not found by Joi so I get returned a status code of 400.

How can I fix my middleware validation to validate both objects within the req object?

from schema validation fails although parameter is available