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我有一个偶尔报告 NullReferenceException 的 MVC3 应用程序。到目前为止，我还无法重现该问题。下面是该函数的编辑版本（以保护无辜者；）以及我在抛出 NullReferenceException 时得到的相应堆栈输出。

[HttpPost]
public ActionResult DoSomething(FormCollection collection)
{
    if (null == collection)
    {
       return RedirectToAction("Index", "Home");
    }

    // other work occurs...


   // NOTE: no problem here accessing collection
   QcModel qcModel = new QcModel (Int32.Parse(collection["Id"]),  collection["Result"]);
   try
   {
       Process(qcModel); // Process() throws some kind of exception
   }
   catch (Exception ex)
   {
        TempData["ValidationError"] = ex.Message;

        // next line is the one that reports the NullReferenceException in stack, aka line 254
        return RedirectToAction("Order", new { Id = Int32.Parse(collection["Id"]), result = collection["Result"], reserved = 0 });
   }

    // additional work if we make it here...
}

到目前为止，基本上我所推断的是，当我们到达我的 catch{} 中突出显示的行时，集合对象为空。现在我无法证明这一点，因为我无法重现这个特定的错误，但我相信这是正在发生的事情，因为在 catch 中生成的异常会冒泡到更高级的处理程序，该处理程序会发送电子邮件给我这个堆栈输出：

Exception: System.NullReferenceException

Error Message: Object reference not set to an instance of an object.

Stack:    at MyWebsite.Controllers.MyController.DoSomething(FormCollection collection) in C:\MyWebsite\Controllers\MyController.cs:line 254
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass15.<InvokeActionMethodWithFilters>b__12()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass15.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass15.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
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)
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