asp.net membership sometmies fails in production - asp.net-mvc-3

Question

I have an ASP.NET MVC 3 application using ASP.NET Membership. I get strange error in production environment. One client complains that they always get an error when they try to log in using Chrome. It works with IE. However for another client they get same error when they log in with IE but works in Chrome.
This is the code for Logon
[HttpPost]
public ActionResult LogOn(LogOnModel model, string returnUrl)
{
if (ModelState.IsValid)
{
if (Membership.ValidateUser(model.UserName, model.Password))
{
FormsAuthentication.SetAuthCookie(model.UserName, model.RememberMe);
if (Url.IsLocalUrl(returnUrl) && returnUrl.Length > 1 && returnUrl.StartsWith("/")
&& !returnUrl.StartsWith("//") && !returnUrl.StartsWith("/\\"))
{
if (returnUrl.Contains("CorporaClaim"))
ViewBag.Layout = _corporaLayout;
else
ViewBag.Layout = _layout;
return Redirect(returnUrl);
}
else
{
ViewBag.Layout = _layout;
// redirect user according to user role
if (!string.IsNullOrEmpty(model.UserName))
return RedirectToDentalinkActionBasedOnRole(model.UserName);
}
}
else
{
ModelState.AddModelError("", "The user name or password provided is incorrect.");
}
}
ViewBag.Layout = _layout;
// If we got this far, something failed, redisplay form
return View(model);
}
In my _Layout.cshtml I make a call to the below method to show the logged in user's name:
#{
string displayName = DentalinkWeb.Utility.LoginUtility.GetDisplayForUser(User);
}
public class LoginUtility
{
public static string GetDisplayForUser(IPrincipal User)
{
string displayName = "";
if (User.Identity.IsAuthenticated)
{
if (User.IsInRole("Practice Admin"))
{
DentalinkEntities db = new DentalinkEntities();
RegisteredPractice prac = (from p in db.RegisteredPractices where p.Email == User.Identity.Name select p).FirstOrDefault();
displayName = prac.DentistFirstName + " " + prac.DentistSurname;
}
else if (User.IsInRole("Dentalink Admin"))
{
displayName = "Dentalink Admin";
}
}
return displayName;
}
}
}
We get this error:
System.NullReferenceException: Object reference not set to an instance of an object.
at DentalinkWeb.Utility.LoginUtility.GetDisplayForUser(IPrincipal User)
at ASP._Page_Views_Shared__Layout_cshtml.Execute() in e:\web\dentalinkco\htdocs\Views\Shared\_Layout.cshtml:line 51
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
at System.Web.WebPages.WebPageBase.<>c__DisplayClass7.<RenderPageCore>b__6(TextWriter writer)
at System.Web.WebPages.HelperResult.WriteTo(TextWriter writer)
at System.Web.WebPages.WebPageBase.Write(HelperResult result)
at System.Web.WebPages.WebPageBase.RenderSurrounding(String partialViewName, Action`1 body)
at System.Web.WebPages.WebPageBase.PopContext()
at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
at System.Web.Mvc.Controller.ExecuteCore()
at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)
at System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext)
at System.Web.Mvc.MvcHandler.<>c__DisplayClass6.<>c__DisplayClassb.<BeginProcessRequest>b__5()
at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass1.<MakeVoidDelegate>b__0()
at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
at System.Web.Mvc.MvcHandler.<>c__DisplayClasse.<EndProcessRequest>b__d()
at System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f)
at System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action)
at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
Please help.

Answer 1

Only thing I can think of will be to add User != null in if statement.
if (User != null && User.Identity.IsAuthenticated)
{
...
RegisteredPractice prac = (from p in db.RegisteredPractices
where p.Email == User.Identity.Name select p).FirstOrDefault();
if(prac != null) // Just to be on safe side.
{
displayName = prac.DentistFirstName + " " + prac.DentistSurname;
}
...
}

Answer 2

Here's a revised code.
public class LoginUtility
{
public static string GetDisplayForUser(IPrincipal User)
{
string displayName = "";
if (User != null)
{
if (User.Identity.IsAuthenticated)
{
if (User.IsInRole("Practice Admin"))
{
DentalinkEntities db = new DentalinkEntities();
RegisteredPractice prac = (from p in db.RegisteredPractices where p.Email == User.Identity.Name select p).FirstOrDefault();
displayName = prac.DentistFirstName + " " + prac.DentistSurname;
}
else if (User.IsInRole("Dentalink Admin"))
{
displayName = "Dentalink Admin";
}
}
}
return displayName;
}
}