HttpClient.SendAsync throwing nullreference exception on http 204

Question

In a .Net 4.7.1 targeted application I am using HttpClient to perform Http requests.

When performing a GET request for a URL that returns a Http 204 result (no content), this results in a System.NullReferenceException: 'Object reference not set to an instance of an object.'.

On top of that, the exception is not caught by the try catch, which I think has something to do with the async call, as specified in this question: Why can't I catch an exception from async code?, but I want to focus on not getting the exception in the first place.

The same request was tested in a .Net Core application using IHttpClientFactory where it works as expected.

protected async Task<HttpResponseMessage> GetResponse(string path, Dictionary<string, string> headers)

    {

        HttpResponseMessage responseMessage = null;
        var request = new HttpRequestMessage(HttpMethod.Get, path);

        if (headers != null)
        {
            foreach (var header in headers)
            {
                request.Headers.Add(header.Key, header.Value);
            }
        }

            var proxy = new WebProxy
            {
                Address = new Uri($"http://{ProxyHost}:{ProxyPort}"),
                BypassProxyOnLocal = false,
                UseDefaultCredentials = false,
                Credentials = new NetworkCredential(userName: ProxyUser, password: ProxyPW)
            };

 
            // create a client handler which uses that proxy

            var httpClientHandler = new HttpClientHandler
            {
                Proxy = proxy
            };

            var httpclient = new HttpClient(httpClientHandler);

            try
            {
                responseMessage = await httpclient.SendAsync(request);
            }
            catch (Exception ex)
            {
                // handle error …
            }

        return responseMessage;

    }

The line throwing the exception is:

responseMessage = await httpclient.SendAsync(request);

Visual Studio catches the unhandled exception:

Exception details:

System.NullReferenceException

  HResult=0x80004003

  Message=Object reference not set to an instance of an object.

  Source=mscorlib

  StackTrace:

   at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task& currentTask)

--- End of stack trace from previous location ---

   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()

   at System.Threading.ThreadPoolWorkQueue.Dispatch()

 

  This exception was originally thrown at this call stack:

    [External Code]

An exception with StackTrace is visible in Event Viewer, but it doesn't help me a lot:

StackTrace:    at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext)

   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)

   at System.Web.LegacyAspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)

   at System.Web.LegacyAspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)

   at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task& currentTask)

--- End of stack trace from previous location where exception was thrown ---

   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()

   at System.Threading.ThreadPoolWorkQueue.Dispatch()

How can I make HttpClient handle the response correctly? I have no control over the server sending the Http 204 response.