asp.net mvc - Object reference not set Error, On Return to Plugins/PaymentPayPalStandard/PDTHandler after payment from paypal -

1. i setup pdt token in nopcommerece site paypall payment.
2. i setup return url of http://www.example.com/plugins/paymentpaypalstandard/pdthandler @ paypal configuration.

i check out successfuly, when time come page. gives me following exception.

---

object reference not set instance of object.

description: unhandled exception occurred during execution of current web request. please review stack trace more information error , originated in code.

exception details: system.nullreferenceexception: object reference not set instance of object.

source error:

the source code generated unhandled exception can shown when compiled in debug mode. enable this, please follow 1 of below steps, request url:

1. add "debug=true" directive @ top of file generated error. example:

or:

2) add following section configuration file of application:

   <compilation debug="true"/> 

note second technique cause files within given application compiled in debug mode. first technique cause particular file compiled in debug mode.

important: running applications in debug mode incur memory/performance overhead. should make sure application has debugging disabled before deploying production scenario.

stack trace:

[nullreferenceexception: object reference not set instance of object.] nop.plugin.payments.paypalstandard.paypalstandardpaymentprocessor.getpdtdetails(string tx, dictionary2& values, string& response) +178 nop.plugin.payments.paypalstandard.controllers.paymentpaypalstandardcontroller.pdthandler(formcollection form) +262 lambda_method(closure , controllerbase , object[] ) +138 system.web.mvc.reflectedactiondescriptor.execute(controllercontext controllercontext, idictionary2 parameters) +228 system.web.mvc.controlleractioninvoker.invokeactionmethod(controllercontext controllercontext, actiondescriptor actiondescriptor, idictionary2 parameters) +34 system.web.mvc.async.asynccontrolleractioninvoker.<begininvokesynchronousactionmethod>b__39(iasyncresult asyncresult, actioninvocation innerinvokestate) +38 system.web.mvc.async.wrappedasyncresult2.callenddelegate(iasyncresult asyncresult) +70 system.web.mvc.async.asynccontrolleractioninvoker.endinvokeactionmethod(iasyncresult asyncresult) +41 system.web.mvc.async.asyncinvocationwithfilters.b__3f() +71 system.web.mvc.async.<>c__displayclass48.b__41() +386 system.web.mvc.async.<>c__displayclass48.b__41() +386 system.web.mvc.async.<>c__displayclass48.b__41() +386 system.web.mvc.async.<>c__displayclass48.b__41() +386 system.web.mvc.async.<>c__displayclass48.b__41() +386 system.web.mvc.async.asynccontrolleractioninvoker.endinvokeactionmethodwithfilters(iasyncresult asyncresult) +42 system.web.mvc.async.<>c__displayclass2b.b__1c() +38 system.web.mvc.async.<>c__displayclass21.b__1e(iasyncresult asyncresult) +186 system.web.mvc.async.asynccontrolleractioninvoker.endinvokeaction(iasyncresult asyncresult) +38 system.web.mvc.controller.b__1d(iasyncresult asyncresult, executecorestate innerstate) +29 system.web.mvc.async.wrappedasyncvoid1.callenddelegate(iasyncresult asyncresult) +67 system.web.mvc.controller.endexecutecore(iasyncresult asyncresult) +53 system.web.mvc.async.wrappedasyncvoid1.callenddelegate(iasyncresult asyncresult) +36 system.web.mvc.controller.endexecute(iasyncresult asyncresult) +38 system.web.mvc.mvchandler.b__5(iasyncresult asyncresult, processrequeststate innerstate) +44 system.web.mvc.async.wrappedasyncvoid`1.callenddelegate(iasyncresult asyncresult) +67 system.web.mvc.mvchandler.endprocessrequest(iasyncresult asyncresult) +38 system.web.callhandlerexecutionstep.system.web.httpapplication.iexecutionstep.execute() +524 system.web.httpapplication.executestep(iexecutionstep step, boolean& completedsynchronously) +167

i not sure but, once used paypalstandard plugin in nopcom.

i found few things,
1. parameter's set paypal differ assumed in nopcom plugin.
2. have received response without data when tried.

so need either change response handler code or try use paypal api first understand structure.