WC_Abstract_Legacy_Order::__isset PHP Method

    public function __isset($key)
    {
        // Legacy properties which could be accessed directly in the past.
        $legacy_props = array('completed_date', 'id', 'order_type', 'post', 'status', 'post_status', 'customer_note', 'customer_message', 'user_id', 'customer_user', 'prices_include_tax', 'tax_display_cart', 'display_totals_ex_tax', 'display_cart_ex_tax', 'order_date', 'modified_date', 'cart_discount', 'cart_discount_tax', 'order_shipping', 'order_shipping_tax', 'order_total', 'order_tax', 'billing_first_name', 'billing_last_name', 'billing_company', 'billing_address_1', 'billing_address_2', 'billing_city', 'billing_state', 'billing_postcode', 'billing_country', 'billing_phone', 'billing_email', 'shipping_first_name', 'shipping_last_name', 'shipping_company', 'shipping_address_1', 'shipping_address_2', 'shipping_city', 'shipping_state', 'shipping_postcode', 'shipping_country', 'customer_ip_address', 'customer_user_agent', 'payment_method_title', 'payment_method', 'order_currency');
        return $this->get_id() ? in_array($key, $legacy_props) || metadata_exists('post', $this->get_id(), '_' . $key) : false;
    }