[Flutter] java.lang.NullPointerException on flutter in app purchase package?

I am trying to integrate in_app_purchase package into my flutter projects. I am using this package because I have my own backend server for verifying purchase. But after integrating I am getting one error. I try to search on the internet but not getting any similar issues, what I am facing. Please from this community help me.

Following is my code-

class SubscriptionPage extends StatefulWidget {
const SubscriptionPage({super.key});

@override
State<SubscriptionPage> createState() => _SubscriptionPageState();
}

class _SubscriptionPageState extends State<SubscriptionPage> {
final InAppPurchase _inAppPurchase = InAppPurchase.instance;
late StreamSubscription<List<PurchaseDetails>> _subscription;

//Product Listing
static const List<String> _productIds = [
'com.fitnesschallengeuk.subscription'
];

@override
void initState() {
final Stream<List<PurchaseDetails>> purchaseUpdated =
_inAppPurchase.purchaseStream;
_subscription =
purchaseUpdated.listen((List<PurchaseDetails> purchaseDetailsList) {
if (mounted) {
_listenToPurchaseUpdated(purchaseDetailsList, context);
}
}, onDone: () {
_subscription.cancel();
}, onError: (Object error) {
if (mounted) {
showSnackBar(context, 'Something went wrong', Severity.error);
}
});
super.initState();
}

Future<Subscription> getProducts() async {
final bool isAvailable = await _inAppPurchase.isAvailable();
if (!isAvailable) {
return Subscription(
isAvailable: isAvailable,
products: [],
notFoundIds: [],
);
}
final ProductDetailsResponse productDetailResponse =
await _inAppPurchase.queryProductDetails(_productIds.toSet());

if (productDetailResponse.error != null) {
throw Exception(productDetailResponse.error!.message);
}
return Subscription(
isAvailable: isAvailable,
products: productDetailResponse.productDetails,
notFoundIds: productDetailResponse.notFoundIDs,
);
}

@override
void dispose() {
_subscription.cancel();
super.dispose();
}

@override
Widget build(BuildContext context) {
var media = MediaQuery.of(context).size;
return Scaffold(
appBar: const BasicAppBar(
title: 'Subscription',
isBack: true,
level: '3',
),
body: QueryBuilder(
query: Query(
key: ['subscription'],
queryFn: () => getProducts(),
config: QueryConfig(
storeQuery: false,
cacheDuration: const Duration(milliseconds: 500),
),
),
builder: (context, state) {
if (state.status == QueryStatus.loading) {
return const Center(
child: SizedBox(
width: 25,
height: 25,
child: CircularProgressIndicator(
color: AppColors.primaryOrange,
strokeWidth: 3,
),
),
);
}
if (state.status == QueryStatus.error) {
return SizedBox(
width: media.width,
child: Text(
state.error.toString(),
style: const TextStyle(
fontSize: 14,
fontWeight: FontWeight.w500,
color: Colors.red,
),
textAlign: TextAlign.center,
),
);
}
final product = state.data!.products[0];
return Padding(
padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 10),
child: SizedBox(
width: media.width,
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Text(
product.title
.replaceAll(
'(com.fitnesschallengeuk.fitness_challenge_uk (unreviewed))',
'')
.trim(),
style: const TextStyle(
fontSize: 16,
),
textAlign: TextAlign.center,
),
SizedBox(height: media.height * 0.06),
SvgPicture.asset(
AppVectors.subscriptionIcon,
width: 260,
),
SizedBox(height: media.height * 0.065),
Text(
product.price,
style: const TextStyle(
fontSize: 35,
fontWeight: FontWeight.w600,
),
),
const Text('/month'),
SizedBox(height: media.height * 0.06),
Text(
product.description,
style: const TextStyle(
fontSize: 13,
),
textAlign: TextAlign.center,
),
const Spacer(),
const Text(
'Are you want to subscribe?',
style: TextStyle(
fontSize: 14,
fontWeight: FontWeight.w600,
),
textAlign: TextAlign.center,
),
const SizedBox(height: 30),
BasicAppButton(
title: 'Subscribe',
onPressed: () {
final PurchaseParam param =
PurchaseParam(productDetails: product);
_inAppPurchase.buyConsumable(purchaseParam: param);
},
level: '3',
),
const SizedBox(height: 20),
],
),
),
);
},
),
);
}

_listenToPurchaseUpdated(
List<PurchaseDetails> purchaseDetailsList, BuildContext context) async {
for (final PurchaseDetails purchaseDetails in purchaseDetailsList) {
if (purchaseDetails.status == PurchaseStatus.pending) {
showSnackBar(
context,
'You are purchasing a subscription',
Severity.success,
);
} else if (purchaseDetails.status == PurchaseStatus.error) {
showSnackBar(
context,
'Your purchased failed!',
Severity.error,
);
} else if (purchaseDetails.status == PurchaseStatus.purchased) {
print('ProductId: ${purchaseDetails.productID}');
print('PurchaseId: ${purchaseDetails.purchaseID}');
print('TransactionId: ${purchaseDetails.transactionDate}');
print(
'Local: ${purchaseDetails.verificationData.localVerificationData}');
print(
'Server: ${purchaseDetails.verificationData.serverVerificationData}');
print('Source: ${purchaseDetails.verificationData.source}');
showSnackBar(
context,
'Your purchase is successfully',
Severity.success,
);
}
}
}
}


Now I am facing one error on my debug_console-

W/BillingLogger( 7906): Unable to log.
W/BillingLogger( 7906): java.lang.NullPointerException


Here is the full screenshot-

Click to see image

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