title: SignalR: Internal Server Error when calling hub method
body: <p>I've been playing around with SignalR for a few days and I have to say that it's an absolutely phenomenal library. I've managed to get a few things working with it and was astounded at the simplicity, but I recently ran into a small problem.</p>
  
  <p>I'm unable to call a Hub method from JavaScript in the browser. The request returns a 500 error code, and when I look at the error page source, I see this:</p>
  
  <pre><code>[ArgumentNullException: Value cannot be null.
  Parameter name: s]
  System.IO.StringReader..ctor(String s) +10207225
  Newtonsoft.Json.Linq.JObject.Parse(String json) +74
  SignalR.Hubs.HubRequestParser.Parse(String data) +78
  SignalR.Hubs.HubDispatcher.OnReceivedAsync(IRequest request, String connectionId,  String data) +266
  SignalR.&lt;&gt;c__DisplayClass6.&lt;ProcessRequestAsync&gt;b__4(String data) +84
  SignalR.Transports.ForeverTransport.ProcessSendRequest() +159
  SignalR.Transports.ForeverTransport.ProcessRequestCore(ITransportConnection connection)  +149
  SignalR.Transports.ForeverTransport.ProcessRequest(ITransportConnection connection) +42
  SignalR.PersistentConnection.ProcessRequestAsync(HostContext context) +1087
  SignalR.Hubs.HubDispatcher.ProcessRequestAsync(HostContext context) +251
  SignalR.Hosting.AspNet.AspNetHandler.ProcessRequestAsync(HttpContextBase context) +656
  SignalR.Hosting.AspNet.HttpTaskAsyncHandler.System.Web.IHttpAsyncHandler.BeginProcessReques t(HttpContext context, AsyncCallback cb, Object extraData) +143
  System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()  +9479007
  System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp;  completedSynchronously) +178
  </code></pre>
  
  <p>My server-side code is:</p>
  
  <pre><code>public class SourceHub : Hub
  {
      public void RegisterSource(string source)
      {
          Groups.Add(Context.ConnectionId, source);
      }
  }
  </code></pre>
  
  <p>and on the client-side I have:</p>
  
  <pre><code>var SourceHub = $.connection.sourceHub;
  $.connection.hub.start().done(function () {
      SourceHub.registerSource("test");
  });
  </code></pre>
  
  <p>I've been digging for a while, but I just can't find the source of the problem... could someone please help me out?</p>