public function get_shipping_classes()
{
if (empty($this->shipping_classes)) {
$classes = get_terms('product_shipping_class', array('hide_empty' => '0', 'orderby' => 'name'));
$this->shipping_classes = !is_wp_error($classes) ? $classes : array();
}
return apply_filters('woocommerce_get_shipping_classes', $this->shipping_classes);
}