public function addError($error = null, $productName = null)
{
$this->errors[] = $error;
$this->session->getFlashBag()->add('eccube.front.request.error', $error);
if (!is_null($productName)) {
$this->session->getFlashBag()->add('eccube.front.request.product', $productName);
}
return $this;
}