Fixed an issue (SignalR#1655) with null values failing to serialize due to an ArgumentNullException.

The code has been modified to use the orinal JToken.FromObject() method if the argument is not null, otherwise JValue.CreateNull() is used instead.

Author: Adam Goss

src/Microsoft.AspNet.SignalR.Client/Hubs/HubProxy.cs

@@ -1,13 +1,11 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.md in the project root for license information.
 
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Globalization;
 using System.Threading.Tasks;
-using Microsoft.AspNet.SignalR.Client;
-using Newtonsoft.Json;
-using Newtonsoft.Json.Linq;
 
 namespace Microsoft.AspNet.SignalR.Client.Hubs
 {
@@ -97,7 +95,9 @@ public Task<TResult> Invoke<TResult, TProgress>(string method, Action<TProgress>
             var tokenifiedArguments = new JToken[args.Length];
             for (int i = 0; i < tokenifiedArguments.Length; i++)
             {
-                tokenifiedArguments[i] = JToken.FromObject(args[i], JsonSerializer);
+                tokenifiedArguments[i] = args[i] != null
+                    ? JToken.FromObject(args[i], JsonSerializer)
+                    : JValue.CreateNull();
             }
 
             var tcs = new TaskCompletionSource<TResult>();