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;
}