i am getting an error like this., result="HeaderMessage\":\"Failure - Object reference not set to an instance of an object"

Question

here is my code...,

Walterkluver request = new Walterkluver();
request = CreateSalesTaxRequest();
ServiceReference1.SureTaxSoapClient oClient = new 
ServiceReference1.SureTaxSoapClient();
tring value=JsonConvert.SerializeObject(request);
result = oClient.PostRequest(value);
return result;


public Walterkluver CreateSalesTaxRequest()
    {

        Walterkluver request = new Walterkluver();
        Item item = new Item();
        WKAddress address = new WKAddress();
        item.BillingAddress = address;
        item.P2PAddress = item.BillingAddress;
        item.ShipToAddress = address;
        item.ShipFromAddress = item.ShipToAddress;
        item.OrderApprovalAddress = item.ShipToAddress;
        item.OrderPlacementAddress = item.ShipToAddress;
        request.itemlist.Add(item);
        return request;
    }