Post an empty body to REST API via HttpClient

Use StringContent or ObjectContent which derive from HttpContent or you can use null as HttpContent:

var response = await client.PostAsync(requestUri, null);

Did this before, just keep it simple:

Task<HttpResponseMessage> task = client.PostAsync(url, null);

Have found that:

Task<HttpResponseMessage> task = client.PostAsync(url, null);

Adds null to the request body, which failed on WSO2. Replaced with:

Task<HttpResponseMessage> task = client.PostAsync(url, new {});

And worked.

To solve this problem, use this example:

   using (var client = new HttpClient())
            {
                var stringContent = new StringContent(string.Empty);
                stringContent.Headers.ContentType = MediaTypeHeaderValue.Parse("application/x-www-form-urlencoded");
                var response = client.PostAsync(url, stringContent).Result;
                var result = response.Content.ReadAsAsync<model>().Result;
            }

I think it does that automagically if your web method has no parameters or they all fit into URL template.

For example this declaration sends empty body:

  [OperationContract]
  [WebGet(UriTemplate = "mykewlservice/{emailAddress}",
     RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json,
     BodyStyle = WebMessageBodyStyle.Wrapped)]
  void GetStatus(string emailAddress, out long statusMask);