private HttpContent CreateRsvpContent(Rsvp rsvpToUpdate)
{
DataContractSerializer singleSerializer = new DataContractSerializer(typeof(Rsvp));
HttpContent content = rsvpToUpdate.ToContentUsingDataContractSerializer(singleSerializer);
content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/xml");
return content;
}