验证成功后的ServiceStack响应会引发错误。缺什么？

Question

我使用了一个restconsole发布：

http://MyApp/auth/credentials

我的自定义AuthProvider如下：

 public class MyAppCredentialsAuthProvider : CredentialsAuthProvider
{

    public override bool TryAuthenticate(IServiceBase authService,
    string userName, string password)
    {         
        //Add here your custom auth logic (database calls etc)
        //Return true if credentials are valid, otherwise false

        SetUp();

        var userDao = _appHost.Container.Resolve<IUserDao>();
        bool isValid = false;

        if (string.IsNullOrEmpty(userName))
            return false;

        if (string.IsNullOrEmpty(password))
            return false;

        var user = userDao.GetUserByUsername(userName);

        if (user == null)
            return false;

        if (string.IsNullOrEmpty(user.Password))
            return false;

        if (CheckPassword(password, user.Password))
        {
            bool isApproved = user.IsApproved;
            if (isApproved && user.Status == (short)Status.Active)
            {
                isValid = true;
                user.IsOnLine = true;
                user.LastLoginDate = DateTime.Now;
                userDao.Update(user);
            }
        }
        return isValid;
    }

    public override void OnAuthenticated(IServiceBase authService,
        IAuthSession session, IOAuthTokens tokens,
        Dictionary<string, string> authInfo)
    {
        try
        {
            // Authenticate the user.
            var userRepo = authService.TryResolve<IUserDao>();
            var user = userRepo.GetUserByUsername(session.UserAuthName);

            session.LastName = user.Lastname;
            session.UserName = user.Username;
            session.Email = user.UserEmail;
            session.DisplayName = user.Lastname + " " + user.Othernames;
            session.IsAuthenticated = true;

            //Important: You need to save the session!
            SessionExpiry = new TimeSpan(0, 5, 0);
            authService.SaveSession(session, SessionExpiry);
        }
        catch (Exception exc)
        {
            // log error
        }

    }


    public void SetUp()
    {
        _appHost = new BasicAppHost().Init();
        var container = _appHost.Container;

        var dbFactory = new OrmLiteConnectionFactory(ConfigurationManager.ConnectionStrings["MyAppDB"].ConnectionString, SqlServerDialect.Provider);
        container.Register<IDbConnectionFactory>(dbFactory);
        container.RegisterAutoWiredAs<UserDao, IUserDao>();            
    }
    }

执行后存在公共覆盖void OnAuthenticated（...）

我收到以下错误：

Server Error in '/' Application.
Object reference not set to an instance of an object.

Stack Trace: 


[NullReferenceException: Object reference not set to an instance of an object.]
   ServiceStack.WebHost.Endpoints.Support.EndpointHandlerBase.HandleException(IHttpRequest httpReq, IHttpResponse httpRes, String operationName, Exception ex) +206
   ServiceStack.WebHost.Endpoints.RestHandler.ProcessRequest(IHttpRequest httpReq, IHttpResponse httpRes, String operationName) +1058
   ServiceStack.WebHost.Endpoints.Support.EndpointHandlerBase.ProcessRequest(HttpContext context) +264
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +341
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69

我错过了哪些参数或配置或步骤？

感谢。