我如何找到RestSharp PUT引發異常的原因？

我已經發出了PUT請求，並在RestSharp.Portable了NullReferenceException：我如何找到RestSharp PUT引發異常的原因？

using (var client = new RestClient(new Uri(BaseUri))) 
{ 
    var oAuth1Authenticator = OAuth1Authenticator.ForAccessToken(
     OAuthConsumerKey, 
     OAuthConsumerSecret, 
     oAuthToken", 
     oAuthSecret" 
    ); 

    client.Authenticator = oAuth1Authenticator; 

    var request = new RestRequest(lastPartUri, httpMethod); 

    request.AddJsonBody(body); 

    IRestResponse response = await client.Execute(request); 

    return response.Content; 
}

IRestResponse response = await client.Execute(request);行拋出的異常。

OAuth params絕對不是null，也不是BaseUri和lastPartUri。 body是Dictionary<string, string>，也不爲空。

POST和GET具有相同參數的請求工作得很好。

貌似問題出在RestSharp庫。我怎麼找到它？

這裏是堆棧跟蹤：

at RestSharp.Portable.Authenticators.OAuth1Authenticator.<>c.<AddOAuthData>b__84_3(Parameter p) 
    at System.Linq.Enumerable.WhereListIterator`1.MoveNext() 
    at RestSharp.Portable.Authenticators.OAuth1Authenticator.AddOAuthData(IRestClient client, IRestRequest request, OAuthWorkflow workflow) 
    at RestSharp.Portable.Authenticators.OAuth1Authenticator.PreAuthenticate(IRestClient client, IRestRequest request, ICredentials credentials) 
    at RestSharp.Portable.RestClientBase.<ExecuteRequest>d__67.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- 
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) 
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) 
    at RestSharp.Portable.HttpClient.RestClient.<Execute>d__5.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- 
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) 
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) 
    at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() 
    at Store.Helpers.MyBookApiConnector.<SendRequest>d__6.MoveNext() 
--- End of stack trace from previous location where exception was thrown --- 
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) 
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) 
    at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult() 
    at Store.Services.DataService.<UpdateReview>d__80.MoveNext()