public string Serialize()
{
string xml = "\r\n<litleToken>" + SecurityElement.Escape(litleToken) + "</litleToken>";
if (expDate != null) xml += "\r\n<expDate>" + SecurityElement.Escape(expDate) + "</expDate>";
if (cardValidationNum != null) xml += "\r\n<cardValidationNum>" + SecurityElement.Escape(cardValidationNum) + "</cardValidationNum>";
if (typeSet) xml += "\r\n<type>" + methodOfPaymentSerializer.Serialize(typeField) + "</type>";
return xml;
}