知道我的NHibernate逻辑有什么问题吗？ (可能是会话管理,不确定)

[AssertionFailure: null id in Lokad.Translate.Entities.User entry (don’t flush the Session after an exception occurs)]
NHibernate.Event.Default.DefaultFlushEntityEventListener.CheckId(Object obj,IEntityPersister persister,Object id,EntityMode entityMode) +292
NHibernate.Event.Default.DefaultFlushEntityEventListener.GetValues(Object entity,EntityEntry entry,EntityMode entityMode,Boolean mightBeDirty,ISessionImplementor session) +93
NHibernate.Event.Default.DefaultFlushEntityEventListener.OnFlushEntity(FlushEntityEvent event) +158
NHibernate.Event.Default.AbstractFlushingEventListener.FlushEntities(FlushEvent event) +469
NHibernate.Event.Default.AbstractFlushingEventListener.FlushEverythingToExecutions(FlushEvent event) +339
NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) +85
NHibernate.Impl.SessionImpl.Flush() +275
NHibernate.Transaction.AdoTransaction.Commit() +236
Lokad.Translate.Repositories.PageRepository.Create(Page page)
Lokad.Translate.Controllers.PagesController.Create(Page page)
lambda_method(ExecutionScope,ControllerBase,Object[] ) +69
System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext,IDictionary2 parameters) +251
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext,ActionDescriptor actionDescriptor,IDictionary2 parameters) +31
System.Web.Mvc.<>c__DisplayClassa.b__7() +88
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter,ActionExecutingContext preContext,Func1 continuation) +534
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext,IList1 filters,IDictionary`2 parameters) +312
System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext,String actionName) +856
System.Web.Mvc.Controller.ExecuteCore() +185
System.Web.Mvc.MvcHandler.ProcessRequest(HttpContextBase httpContext) +221
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +586
System.Web.HttpApplication.ExecuteStep(IExecutionStep step,Boolean& completedSynchronously) +177

请注意,我使用的是_session.FlushMode = FlushMode.Commit;并且用户在自定义RoleProvider中使用

public class SimpleRoleProvider : RoleProvider 
{
    readonly UserRepository Users = new UserRepository();

    public override string[] GetRolesForUser(string username)
    {
        try
        {
            var user = Users.Get(username);

            // no role if user is not registered
            if (null == user) return new string[0];

            // default role for registered user
            return user.IsManager ? new[] { "Manager","User" } : new[] { "User" };
        }
        catch (Exception)
        {
            // role should not fail in case of DB issue.
            return new string[0];
        }
    }
}