Impossible d'accéder au champ attribué au champ d'un élément de travail DevOps Azure

Je crée une application de console dans Visual Studio pour obtenir les détails de l'élément de travail à partir d'un projet Azure Devops. Je ne suis pas en mesure d'accéder au champ code> attribué code> d'un élément de travail.

J'ai essayé d'utiliser le code dans Microsoft Page pour interroger des éléments de travail avec quelques modifications et son affichage d'une exception lorsque j'essaie d'accéder au champ attribué code>. p>

static void Main(string[] args)
{
    string _uri = "https://dev.azure.com/xyz";
     string _personalAccessToken = 
     "xpdrix7nyspotj3l4gotvvk4cpp2z6l65g5r";
     string _project = "FirstProject";
     Uri uri = new Uri(_uri);
     string personalAccessToken = _personalAccessToken;
     string project = _project;

     VssBasicCredential credentials = new VssBasicCredential("", 
     _personalAccessToken);

     //create a wiql object and build our query
     Wiql wiql = new Wiql()
     {
         Query = "Select *" +
                 "From WorkItems " +
                 "Where [System.TeamProject] = '" + project + "' " +
                  "Order By [State] Asc, [Changed Date] Desc"
     };

     //create instance of work item tracking http client
      sing (WorkItemTrackingHttpClient workItemTrackingHttpClient = 
      new WorkItemTrackingHttpClient(uri, credentials))
      {
         //execute the query to get the list of work items in the results 
         WorkItemQueryResult workItemQueryResult = 
         workItemTrackingHttpClient.QueryByWiqlAsync(wiql).Result;

         //some error handling                
         if (workItemQueryResult.WorkItems.Count() != 0)
         {
             //need to get the list of our work item id's and put them 
             //into an array
             List<int> list = new List<int>();
             foreach (var item in workItemQueryResult.WorkItems)
             {
                 list.Add(item.Id);
             }
             int[] arr = list.ToArray();

             //build a list of the fields we want to see
             string[] fields = new string[3];
             fields[0] = "System.Id";
             fields[1] = "System.Title";
             fields[2] = "System.AssignedTo";
             WorkItemExpand workItemExpand = WorkItemExpand.All;

             //get work items for the id's found in query
             var workItems = 
             workItemTrackingHttpClient.GetWorkItemsAsync(arr, fields=null, workItemQueryResult.AsOf,workItemExpand).Result;

             Console.WriteLine("Query Results: {0} items found", workItems.Count);

             //loop though work items and write to console
             foreach (var workItem in workItems)
             {
                 Console.WriteLine("{0}{1}{2}", workItem.Id, workItem.Fields["System.Title"], workItem.Fields["System.AssignedTo"]);
             }

          }
       }
    }
}