title: Google Dialogflow V2 webhook not working - InvalidType and Null Exception
body: <p>I'm following google example to create a .net core 3.0 webhook for dialogflow using Google Dailog Flow cersion 2 api.  this is the code</p>
  
  <pre><code>public class DialogflowController : ControllerBase
  {
     private static readonly JsonParser jsonParser =
          new JsonParser(JsonParser.Settings.Default.WithIgnoreUnknownFields(true));
  
      public ContentResult DialogAction()
      {
          WebhookRequest request;
          using (var reader = new StreamReader(Request.Body))
          {
              request = jsonParser.Parse&lt;WebhookRequest&gt;(reader);
          }
  
          // Note: you should authenticate the request here.
  
          // Populate the response
          WebhookResponse response = new WebhookResponse
          {
              // ...
          };
  
          string responseJson = response.ToString();
          return Content(responseJson, "application/json");
      }
  }
  </code></pre>
  
  <p>I'm using SoapUI to create a rest service and test the code using a post request copied from dialogflow itself.  When running I'm receiving the following error:</p>
  
  <pre><code>---&gt; System.TypeInitializationException: The type initializer for 'Google.Cloud.Dialogflow.V2.ContextReflection' threw an exception.
   ---&gt; System.ArgumentNullException: Value cannot be null. (Parameter 'extension')
  </code></pre>
  
  <p>Any ideas why or what I'm missing here?</p>
  
  <p>Thanks</p>