private function getBootstrapPath($path = null)
    {
        if (!$path) {
            $path = dirname($this->getVendorPath()) . '/bootstrap/app.php';
        } elseif (!$this->isAbsolutePath($path)) {
            $path = $this->getVendorPath() . '/' . $path;
        }

        if (!is_file($path)) {
            throw new InvalidArgumentException("App bootstrap at `{$path}` not found.");
        }

        return $path;
    }