public static void AddControls(this XElement element, AddInList list, XNamespace ns)
        {
            var items = list?.ToXml(ns).ToArray();

            if (items != null && items.Any())
            {
                foreach (var item in items)
                {
                    element.Add(item);
                }
            }
        }
        public static void AddControls <T>(this XElement element, AddInList <T> items, XNamespace ns)
            where T : AddInElement
        {
            if (items == null)
            {
                return;
            }

            foreach (var item in items)
            {
                element.Add(item.ToXml(ns));
            }
        }