Got NullReferenceException when Unit testing Controller

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NUnit

MVC3

Hello,

I am working on Unit testing the MVC3 site using NUnit, MvcContrib.TestHelper package but I am facing the exception "Object reference not set to an instance of an object" when my test method accesses the controller having TryUpdateModel. I dont know what to do to pass the test. please help me in this.

I am also giving a code for that :

Action from Controller which test method calls, is given below :

public JsonResult AddPatient()
       {

           bool returnStatus;
           string returnErrorMessage;

           List<string> returnMessage;

           PatientBLL patientBLL = new PatientBLL();

           Models.PatientViewModel patientViewModel = new Models.PatientViewModel();

           TryUpdateModel(patientViewModel);

           Patient patient = patientBLL.AddPatient(
               patientViewModel,
               out returnMessage,
               out returnStatus,
               out returnErrorMessage);

           patientViewModel.UpdateViewModel(patient, typeof(Patient).GetProperties());

           patientViewModel.ReturnMessage = returnMessage;
           patientViewModel.ReturnStatus = returnStatus;

           return Json(patientViewModel);

       }

and the test method which calls the above action is given below :

[Test]
       public void Test_AddPatient()
       {
           TestControllerBuilder builder = new TestControllerBuilder();

           string uniquePatientKey = GenerateUniqueID();

           builder.Form["MedicalID"] = uniquePatientKey;
           builder.Form["SocialSecurityNumber"] = uniquePatientKey;
           builder.Form["FirstName"] = "Khushi";
           builder.Form["LastName"] = "Maahi";
           builder.Form["AddressLine1"] = "ABCD";
           builder.Form["AddressLine2"] = "Technologies";
           builder.Form["City"] = "OOna";
           builder.Form["State"] = "UP";
           builder.Form["ZipCode"] = "98456-7329";
           builder.Form["PhoneNumber"] = "(425)882-8080";
           builder.Form["DateOfBirth"] = "10/28/1987";
           builder.Form["PatientDateOfBirth"] = "10/28/1987";
           builder.Form["EffectiveDate"] = "01/01/1995";
           builder.Form["PatientEffectiveDate"] = "01/01/1995";

           PatientController patientController = builder.CreateController<PatientController>();
          JsonResult jsonResult = (JsonResult)patientController.AddPatient();

           dynamic jsonData = jsonResult.Data;
           string jsonMessage=Convert.ToString(jsonData.ReturnMessage);
           Assert.AreEqual(jsonData.ReturnStatus, true );
           Assert.Greater(jsonData.PatientID, 0);


       }

Please give me the solution for my probelm.