public static Task <StockItem> GetStockItemAsync(this FreeAgentClient client, Uri url)
        {
            var id = url.GetId();

            return(client.GetStockItemAsync(id));
        }
        public static Task <StockItem> GetStockItemAsync(this FreeAgentClient client, StockItem stockItem)
        {
            var id = client.ExtractId(stockItem);

            return(client.GetStockItemAsync(id));
        }