src/Core/Application.php
private function set404()
    {
        $this->response->setStatusCode(404);
        $content = '404 Not Found';
        if (file_exists($this->packageRoot . '/view/404.html.php')) {
            $content = (new Native($this->packageRoot))->getContent('404.html.php');
        }
        $this->response->setContent($content);
    }
private function set404()
    {
        $this->response->setStatusCode(404);
        $content = '404 Not Found';
        if (file_exists($this->packageRoot . '/view/404.html.php')) {
            $content = (new Native($this->packageRoot))->getContent('404.html.php');
        }
        $this->response->setContent($content);
    }
Set 404 code and content.