Uncaught Error: Call to undefined method Error::loadModel()

<?php
 
class Bootstrap 
{
 
    private $_url = null;
    private $controller = null;
 
    private $modelFolder = MODELS_PATH;
    private $controllerFolder = CONTROLLERS_PATH; 
 
    private $errorFile = 'error.php';
    private $indexFile = 'index.php';
 
    public function init()
    {
        $this->getFromUrl();
 
        if (empty($this->_url[0])) 
        {
            $this->loadIndexController();
            return false;
        }
        
        $this->loadExistingController();
        $this->callControllerMethod();
    }
 
    public function setControllerFolder($folder)
    {
        $this->controllerFolder = trim($folder, '/') . '/';
    }
 
    public function setModelFolder($folder)
    {
        $this->modelFolder = trim($folder, '/') . '/';
    }
 
    public function setErrorFile($folder)
    {
        $this->errorFile = trim($folder, '/');
    }
 
    public function setIndexFile($folder)
    {
        $this->indexFile = trim($folder, '/');
    }
 
    private function getFromUrl()
    {
        $url = $_GET['url'] ?? null;
        $url = rtrim($url, '/');
        $url = filter_var($url, FILTER_SANITIZE_URL);
        $this->_url = explode('/', $url);
    }
 
    private function loadIndexController()
    {
        require $this->controllerFolder . $this->indexFile;
        $this->controller = new Index();
        $this->controller->index();
    }
 
    private function loadExistingController()
    {
        $file = $this->controllerFolder . $this->_url[0] . '.php';
 
        if (file_exists($file)) 
        {
            require $file;
 
            $this->controller = new $this->_url[0];
            $this->controller->loadModel($this->_url[0], $this->modelFolder);
        } 
 
        else 
            
        {
            $this->error();
            return false;
        }
    }
 
    private function callControllerMethod()
    {
        $length = count($this->_url);
 
        if ($length > 1) 
        {
            if (!method_exists($this->controller, $this->_url[1])) 
            {
                $this->error();
            }
        }
 
        switch ($length)
        {
            case 5:
 
            $this->controller->{$this->_url[1]}($this->_url[2], $this->_url[3], $this->_url[4]);
            break;
 
            case 4:
 
            $this->controller->{$this->_url[1]}($this->_url[2], $this->_url[3]);
            break;
 
            case 3:
 
            $this->controller->{$this->_url[1]}($this->_url[2]);
            break;
 
            case 2:
 
            $this->controller->{$this->_url[1]}();
            break;
 
            default:
 
            $this->controller->index();
            break;
        }
    }
 
    private function error() 
    {
        require $this->controllerFolder . $this->errorFile;
        $this->controller = new ErrorController();
        $this->controller->error404();
        exit;
    }
 
}

$this->controller = new $this->_url[0];
            $this->controller->loadModel($this->_url[0], $this->modelFolder);

$this->controller = new Error();
            $this->controller->loadModel($this->_url[0], $this->modelFolder);