How does the asp.net mvc framework deals with Null values

Question

I have some problem in understanding how does the asp.net mvc deal with Null values . In the first scenario i have the following action method:-

[HttpPost]
        public ActionResult Delete(int labtestid, int visitid)
        {
try
            {
                var vlr = repository.GetVisitLabResult(labtestid,visitid);
                string desc = vlr.LabTest.Description; 
                repository.DeleteVisitLabResult(vlr);
                repository.Save();
                return Json(new { IsSuccess = "True", id = labtestid, description =    desc }, JsonRequestBehavior.AllowGet);
            }

Incase the repository method var vlr = repository.GetVisitLabResult(labtestid,visitid); does not return any result (var vlr is null) then the following exception will be raised on the string desc = vlr.LabTest.Description; NullReferenceException was unhandled by user code. So why did the framework raise an exception instead of just assigning a null value to the string desc !!! BR

Mathew Thompson · Accepted Answer · 2012-04-30 16:55:20Z

3

It looks like the actual object itself is null. You have a null object and you're trying to access properties on it, hence the runtime will throw a NullReferenceException. You're best off checking if the object is null first before trying to access it's members :)

answered Apr 30, 2012 at 16:55

Mathew Thompson

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