在通过API创建新的工作项时，无法获取TFS for AssignedTo字段中的有效用户列表

Question

您好我正在尝试通过TFS API创建新的工作项，这是我在下面使用的方法，以获取可以分配工作项的有效用户列表。不知何故，它在validUserSids行上给了我一个空引用异常。谁知道这里有什么问题？

private string[] TFSUsers(string server)
    {
        // Get a Reference to Team Foundation Server.
        TeamFoundationServer tfs = tfsdata.GetTFS(server);
        // Get a reference to Group Security Service.
        IGroupSecurityService gss = (IGroupSecurityService)tfs.GetService(typeof(IGroupSecurityService));
        // Resolve to SIDs
        Identity validUserSids = gss.ReadIdentity(SearchFactor.AccountName, "TFS Valid Users", QueryMembership.Expanded);
        // Resolve to actual users
        Identity[] validUsers = gss.ReadIdentities(SearchFactor.Sid, validUserSids.Members, QueryMembership.None);
        List<string> Users = new List<string>();
        foreach (Identity user in validUsers)
        {
            Users.Add(user.DisplayName);
        }
        return Users.ToArray();
    }

Answer 1

以下是如何获取TFS中的用户列表：

var tfs = TeamFoundationServerFactory.GetServer("http://vstspioneer:8080/tfs/VSTSDF");
var workItemStore = (WorkItemStore)tfs.GetService(typeof(WorkItemStore));
var allowedValues = workItemStore.FieldDefinitions[CoreField.AssignedTo].AllowedValues;

foreach (String value in allowedValues)
{
    Console.WriteLine(value);
}