title: Following in app purchase, app crashing on startup. productIdentifier=nil?
body: <p>I have a few users who have reported that after attempting an in app purchase the app is now crashing on startup. I have asked them to delete and reinstall the app which has not worked, and attempted to ask them to go into airplane mode to stop any network communication that has not worked. </p>
  
  <p>I am unable to replicate the error in anyway on my devices and my in app purchase goes through just fine in sandbox and production modes. My thought is that somehow their transaction received a nil productIdentifier which is causing the startup crash but I am not sure what transaction observer methods get called at app startup that I can fix the issue for them.</p>
  
  <p>Is there someway to "clear" the transaction queue or otherwise test for nil productidentifiers on start up and allow these users to get the app at least running again? I've done several hundred in app purchases using the code below and this just recently began happening. Which of the helper methods get called on app startup? </p>
  
  <p>In AppDelegate.m</p>
  
  <pre><code>[[SKPaymentQueue defaultQueue] addTransactionObserver:[MovieClockIAPHelper sharedHelper]];
  </code></pre>
  
  <p>In app helper code:</p>
  
  <pre><code>- (id)initWithProductIdentifiers:(NSSet *)productIdentifiers {
      if ((self = [super init])) {
  
          // Store product identifiers
          _productIdentifiers = [productIdentifiers retain];
  
          // Check for previously purchased products
  
          NSMutableSet * purchasedProducts = [NSMutableSet set];
          for (NSString * productIdentifier in _productIdentifiers) {
  
              BOOL productPurchased = [[NSUserDefaults standardUserDefaults] boolForKey:productIdentifier];
  
              if (productPurchased) {
                  [purchasedProducts addObject:productIdentifier];
                  NSLog(@"Previously purchased: %@", productIdentifier);
              }
              else{
              NSLog(@"Not purchased: %@", productIdentifier);
              }
          }
          self.purchasedProducts = purchasedProducts;
  
      }
      return self;
  }
  
  - (void)requestProducts {
  
      self.request = [[[SKProductsRequest alloc] initWithProductIdentifiers:_productIdentifiers] autorelease];
      _request.delegate = self;
      [_request start];
  
  }
  
  - (void)productsRequest:(SKProductsRequest *)request didReceiveResponse:(SKProductsResponse *)response {
  
      NSLog(@"Received products results...");   
      self.products = response.products;
      self.request = nil;    
  
      [[NSNotificationCenter defaultCenter] postNotificationName:kProductsLoadedNotification object:_products];    
  }
  
  
  - (void)restoreCompletedTransactions {
      [[SKPaymentQueue defaultQueue] restoreCompletedTransactions];
  }
  
  - (void)provideContent:(NSString *)productIdentifier {
  
      NSLog(@"Toggling flag for: %@", productIdentifier);
      [[NSUserDefaults standardUserDefaults] setBool:TRUE forKey:productIdentifier];
      [[NSUserDefaults standardUserDefaults] synchronize];
      [_purchasedProducts addObject:productIdentifier];
  
      [[NSNotificationCenter defaultCenter] postNotificationName:kProductPurchasedNotification object:productIdentifier];
  
  }
  
  - (void)completeTransaction:(SKPaymentTransaction *)transaction {
  
      NSLog(@"completeTransaction...");
  
      [self recordTransaction: transaction];
      [self provideContent: transaction.payment.productIdentifier];
      [[SKPaymentQueue defaultQueue] finishTransaction: transaction];
  
  }
  
  - (void)restoreTransaction:(SKPaymentTransaction *)transaction {
  
      NSLog(@"restoreTransaction...");
  
  
      [self recordTransaction: transaction];
      [self provideContent: transaction.originalTransaction.payment.productIdentifier];
      [[SKPaymentQueue defaultQueue] finishTransaction: transaction];
  
  }
  
  - (void)failedTransaction:(SKPaymentTransaction *)transaction {
  
      if (transaction.error.code != SKErrorPaymentCancelled)
      {
          NSLog(@"Transaction error: %@", transaction.error.localizedDescription);
      }
  
      [[NSNotificationCenter defaultCenter] postNotificationName:kProductPurchaseFailedNotification object:transaction];
  
      [[SKPaymentQueue defaultQueue] finishTransaction: transaction];
  
  }
  
  - (void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions
  {
      NSLog(@"in the payment queue");
  
      for (SKPaymentTransaction *transaction in transactions)
      {
  
          switch (transaction.transactionState)
          {
              case SKPaymentTransactionStatePurchased:
                  [self completeTransaction:transaction];
                  break;
              case SKPaymentTransactionStateFailed:
                  [self failedTransaction:transaction];
                  break;
              case SKPaymentTransactionStateRestored:
                  [self restoreTransaction:transaction];
              default:
                  break;
          }
          }
  
  }
  
  -(void)buyProduct:(SKProduct *)product
  {
      NSLog(@"In buyproduct Buying %@...", product.productIdentifier);
  
      SKPayment *payment = [SKPayment paymentWithProduct:product];
  
      [[SKPaymentQueue defaultQueue] addPayment:payment];
  }
  
  - (void)dealloc
  {
      [_productIdentifiers release];
      _productIdentifiers = nil;
      [_products release];
      _products = nil;
      [_purchasedProducts release];
      _purchasedProducts = nil;
      [_request release];
      _request = nil;
      [super dealloc];
  }
  
  @end
  </code></pre>