ios - in app purchases - device crash -

if run app in simulator says failedtransaction...

and if run on iphone crashes error:

* terminating app due uncaught exception 'nsinvalidargumentexception', reason: '* -[__nssetm addobject:]: object cannot nil'

here: code:

- (uitableviewcell *)tableview:(uitableview *)tableview cellforrowatindexpath:  (nsindexpath *)indexpath { uitableviewcell *cell = [tableview dequeuereusablecellwithidentifier:@"cell" forindexpath:indexpath];  skproduct * product = (skproduct *) _products[indexpath.row]; cell.textlabel.text = product.localizedtitle; [_priceformatter setlocale:product.pricelocale]; cell.detailtextlabel.text = [_priceformatter stringfromnumber:product.price];   if([[scoreboardiaphelper sharedinstance] productpurchased:product.productidentifier]) {      cell.accessorytype = uitableviewcellaccessorycheckmark;     cell.accessoryview = nil; } else {     uibutton *buybutton = [uibutton buttonwithtype:uibuttontyperoundedrect];     buybutton.frame = cgrectmake(0, 0, 72, 37);     [buybutton settitle:@"buy" forstate:uicontrolstatenormal];     buybutton.tag = indexpath.row;     [buybutton addtarget:self action:@selector(buybuttontapped:)  forcontrolevents:uicontroleventtouchupinside];     cell.accessorytype = uitableviewcellaccessorynone;     cell.accessoryview = buybutton; }  return cell; }  - (void)buybuttontapped:(id)sender {  uibutton *buybutton = (uibutton *)sender; skproduct *product = _products[buybutton.tag];  nslog(@"buying %@...", product.productidentifier); [[scoreboardiaphelper sharedinstance] buyproduct:product];  [[nsnotificationcenter defaultcenter] addobserver:self selector:@selector(productpurchased:) name:iaphelperproductpurchasednotification object:nil];    } 

and error here:

- (void)providecontentforproductidentifier:(nsstring *)productidentifier {  [_purchasedproductidentifiers addobject:productidentifier]; [[nsuserdefaults standarduserdefaults] setbool:yes forkey:productidentifier]; [[nsuserdefaults standarduserdefaults] synchronize]; [[nsnotificationcenter defaultcenter] postnotificationname:iaphelperproductpurchasednotification object:productidentifier];   } 

[__nssetm addobject:]: object cannot nil 

this means have mutable set calling addobject: on, variable passing in nil.

in code post, place call in line:

[_purchasedproductidentifiers addobject:productidentifier]; 

...so wherever calling providecontentforproductidentifier:, passing nil.