title: TFS webapi updates failing after updating to latest newtonsoft.json version 11
body: <p>I'm updating Team Foundation work items using the UpdateWorkItemAsync method.  The relevant line of code looks like this:</p>
  
  <pre><code>Microsoft.TeamFoundation.WorkItemTracking.WebApi.Models.WorkItem result = 
  workItemTrackingClient.UpdateWorkItemAsync(patchDocument, id.Value).Result;
  </code></pre>
  
  <p>(I think this will loom familiar to anyone managing TFS workitems with the webapi library)</p>
  
  <p>The sample code I found in github uses newtonsoft.json 9.0.0.0, and works fine. 
   In my project I use newtonsoft.json 11.0.0.0, and the patchdocument fails to serialize (The body of the call is an empty json -  {} ).  And when i upgaded the sample code to version 11 it failed also.</p>
  
  <p>This looks to me like a bug in version 11.0.0.0.  Is there a workaround?  Is there a serialization setting that i need to change?  Any ideas?</p>