Tuto POO en PHP

Bonjour,

Je suis le tutoriel https://www.grafikart.fr/formations/programmation-objet-php et je suis rendu au chapitre 18.
Mais voila, je rencontre un petit problème avec mon code.

Voici mon fichier users.php

<?php
$users = App::getInstance()->getTable('users')->getAll();
?>
<div id="contenu">
    <table>
        <thead>
        <tr>
            <th>
                <a>Nom</a>
            </th>
            <th>
                <a>Nom d'utilisateur</a>
            </th>
            <th>
                <a>Groupe</a>
            </th>
            <th>
                <a>Désactivé</a>
            </th>
        </tr>
        </thead>
        <tbody>
        <?php
        foreach ($users as $user):
        ?>
            <tr id="user_<?= $user->id_user ?>" onclick="window.location.href='<?= $user->url ?>'">
                <td> <?= $user->name_user ?> </td>
                <td> <?= $user->username_user ?> </td>
                <td> <?= $user->name_group ?> </td>
                <td class="boolean">
                    <input type="checkbox" <?= ($user->active_user) ? 'checked' : '' ?> disabled="">
                </td>
            </tr>
        <? endforeach; ?>
        </tbody>
        <tfoot></tfoot>
    </table>
</div>

Ce qui ne fonctionne pas c'est lorsque je fais cette ligne, je me retrouve avec une page blanche.

<?= $user->url ?>

Voici mes autres fichiers:

App.php:

<?php
use Core\Config;
use Core\Database;

class App{
    private static $_instance;
    private $db_instance;

    public static function getInstance(){
        if(is_null(self::$_instance)){
            self::$_instance = new App();
        }
        return self::$_instance;
    }

    public static function load(){
        session_start();
        require ROOT . '/app/Autoloader.php';
        \App\Autoloader::register();
        require ROOT . '/core/Autoloader.php';
        \Core\Autoloader::register();
    }

    public function getTable($name){
        $class_name = '\\App\\Model\\Model' . ucfirst($name);
        return new $class_name($this->getDb());
    }

    public function getDb(){
        $config = Config::getInstance(ROOT . '/config/config.php');
        if(is_null($this->db_instance)){
            $this->db_instance = new Database($config->get('db_name'), $config->get('db_user'), $config->get('db_pass'), $config->get('db_host'));
        }
        return $this->db_instance;
    }
}

ModelUsers.php

<?php
namespace App\Model;

use Core\Model\Model;

class ModelUsers extends Model{
    public function __get($name)
    {
        $method = 'get' . ucfirst($name);
        $this->$name = $this->$method();
        return $this->$name;
    }

    public function getUrl(){
        return 'index.php?p=users.edit&id='. $this->id_user;
    }
}

Model.php

<?php
namespace Core\Model;

use Core\Database;

class Model{

    protected $table;
    protected $db;

    public function __get($name)
    {
        $method = 'get' . ucfirst($name);
        $this->$name = $this->$method();
        return $this->$name;
    }

    public function __construct(Database $db)
    {
        $this->db = $db;
        if(is_null($this->table)){
            $class_parts = explode('\\', get_class($this));
            $class_name = end($class_parts);
            $this->table = strtoupper(str_replace('Model', '', $class_name));
        }
    }

    public  function query($statement, $attributes = null, $one = false){
        if($attributes){
            return $this->db->prepare($statement, $attributes, get_called_class(), $one);
        }else{
            return $this->db->query($statement, get_called_class(), $one);
        }
    }

    public function getAll(){
        return $this->query("SELECT * FROM " . $this->table);
    }
}

Database.php:

<?php
namespace Core;

use \PDO;

class Database
{
    private $db_name;
    private $db_user;
    private $db_pass;
    private $db_host;
    private $pdo;

    public function __construct($db_name, $db_user, $db_pass, $db_host)
    {
        $this->db_name = $db_name;
        $this->db_user = $db_user;
        $this->db_pass = $db_pass;
        $this->db_host = $db_host;
    }

    private function getPDO()
    {
        if ($this->pdo === null) {
            $pdo = new PDO('mysql:dbname=' . $this->db_name . ';host=' . $this->db_host, $this->db_user, $this->db_pass);
            $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $this->pdo = $pdo;
        }
        return $this->pdo;
    }

    public function query($statement, $class_name = null, $one = false)
    {
        $req = $this->getPDO()->query($statement);
        if($class_name === null){
            $req->setFetchMode(PDO::FETCH_OBJ);
        }else{
            $req->setFetchMode(PDO::FETCH_CLASS, $class_name);
        }
        if ($one) {
            $data = $req->fetch();
        } else {
            $data = $req->fetchAll();
        }
        return $data;
    }

    public function prepare($statement, $attributes, $class_name = null, $one = false)
    {
        $req = $this->getPDO()->prepare($statement);
        if($class_name === null){
            $req->setFetchMode(PDO::FETCH_OBJ);
        }else{
            $req->setFetchMode(PDO::FETCH_CLASS, $class_name);
        }
        $req->execute($attributes);
        if ($one){
            return $req->fetch();
        }
        else{
            return $req->fetchAll();
        }
    }
}

Je ne sais pas si vous avez tout ce que vous avez besoin pour m'aider, mais faites le moi savoir.