public static function instance()
 {
     if (is_null(self::$_instance)) {
         self::$_instance = new self();
     }
     return self::$_instance;
 }
 function process_order_meta_box_actions($post)
 {
     $order_id = $post->id;
     $post_status = $post->post_status;
     if ($post_status == 'trash' || $post_status == 'wc-cancelled') {
         return false;
     }
     parent::emitirNFe(array($order_id));
 }