account for null value returned from method channel

packages/in_app_purchase/lib/src/billing_client_wrappers/billing_client_wrapper.dart

@@ -113,7 +113,7 @@ class BillingClient {
             <String, dynamic>{
           'handle': disconnectCallbacks.length - 1,
           'enablePendingPurchases': _enablePendingPurchases
-        }))!);
+        })) ?? <String, dynamic>{});
   }
 
   /// Calls
@@ -145,7 +145,7 @@ class BillingClient {
     return SkuDetailsResponseWrapper.fromJson((await channel.invokeMapMethod<
             String, dynamic>(
         'BillingClient#querySkuDetailsAsync(SkuDetailsParams, SkuDetailsResponseListener)',
-        arguments))!);
+        arguments)) ?? <String, dynamic>{});
   }
 
   /// Attempt to launch the Play Billing Flow for a given [skuDetails].
@@ -181,7 +181,7 @@ class BillingClient {
     return BillingResultWrapper.fromJson(
         (await channel.invokeMapMethod<String, dynamic>(
             'BillingClient#launchBillingFlow(Activity, BillingFlowParams)',
-            arguments))!);
+            arguments)) ?? <String, dynamic>{});
   }
 
   /// Fetches recent purchases for the given [SkuType].
@@ -201,7 +201,7 @@ class BillingClient {
         .invokeMapMethod<String, dynamic>(
             'BillingClient#queryPurchases(String)', <String, dynamic>{
       'skuType': SkuTypeConverter().toJson(skuType)
-    }))!);
+    })) ?? <String, dynamic>{});
   }
 
   /// Fetches purchase history for the given [SkuType].
@@ -222,7 +222,7 @@ class BillingClient {
     return PurchasesHistoryResult.fromJson((await channel.invokeMapMethod<
             String, dynamic>(
         'BillingClient#queryPurchaseHistoryAsync(String, PurchaseHistoryResponseListener)',
-        <String, dynamic>{'skuType': SkuTypeConverter().toJson(skuType)}))!);
+        <String, dynamic>{'skuType': SkuTypeConverter().toJson(skuType)})) ?? <String, dynamic>{});
   }
 
   /// Consumes a given in-app product.
@@ -242,7 +242,7 @@ class BillingClient {
             <String, dynamic>{
           'purchaseToken': purchaseToken,
           'developerPayload': developerPayload,
-        }))!);
+        }))??<String, dynamic>{});
   }
 
   /// Acknowledge an in-app purchase.
@@ -273,7 +273,7 @@ class BillingClient {
         <String, dynamic>{
           'purchaseToken': purchaseToken,
           'developerPayload': developerPayload,
-        }))!);
+        }))??<String, dynamic>{});
   }
 
   /// The method call handler for [channel].

packages/in_app_purchase/lib/src/billing_client_wrappers/sku_details_wrapper.dart

@@ -13,6 +13,11 @@ import 'enum_converters.dart';
 // rebuild and watch for further changes.
 part 'sku_details_wrapper.g.dart';
 
+/// The error message shown when the map represents billing result is invalid from method channel.
+///
+/// This usually indicates a series underlining code issue in the plugin.
+const kInvalidBillingResultErrorMessage = 'Invalid billing result map from method channel.';
+
 /// Dart wrapper around [`com.android.billingclient.api.SkuDetails`](https://developer.android.com/reference/com/android/billingclient/api/SkuDetails).
 ///
 /// Contains the details of an available product in Google Play Billing.
@@ -208,8 +213,12 @@ class BillingResultWrapper {
   ///
   /// The map needs to have named string keys with values matching the names and
   /// types of all of the members on this class.
-  factory BillingResultWrapper.fromJson(Map<String, dynamic> map) =>
-      _$BillingResultWrapperFromJson(map);
+  factory BillingResultWrapper.fromJson(Map<String, dynamic>? map) {
+      if (map == null || map.isEmpty) {
+        return BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage);
+      }
+      return _$BillingResultWrapperFromJson(map);
+  }
 
   /// Response code returned in the Play Billing API calls.
   final BillingResponse responseCode;

packages/in_app_purchase/lib/src/store_kit_wrappers/sk_payment_queue_wrapper.dart

@@ -46,7 +46,7 @@ class SKPaymentQueueWrapper {
 
   /// Calls [`-[SKPaymentQueue canMakePayments:]`](https://developer.apple.com/documentation/storekit/skpaymentqueue/1506139-canmakepayments?language=objc).
   static Future<bool> canMakePayments() async =>
-      (await channel.invokeMethod<bool>('-[SKPaymentQueue canMakePayments:]'))!;
+      (await channel.invokeMethod<bool>('-[SKPaymentQueue canMakePayments:]')) ?? false;
 
   /// Sets an observer to listen to all incoming transaction events.
   ///

packages/in_app_purchase/test/billing_client_wrappers/billing_client_wrapper_test.dart

@@ -96,6 +96,19 @@ void main() {
           equals(
               <dynamic, dynamic>{'handle': 0, 'enablePendingPurchases': true}));
     });
+
+    test('handles method channel returning null', () async {
+      stubPlatform.addResponse(
+        name: methodName,
+        value: null,
+      );
+
+      expect(
+          await billingClient.startConnection(
+              onBillingServiceDisconnected: () {}),
+          equals(BillingResultWrapper(
+          responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+    });
   });
 
   test('endConnection', () async {
@@ -151,6 +164,19 @@ void main() {
       expect(response.billingResult, equals(billingResult));
       expect(response.skuDetailsList, contains(dummySkuDetails));
     });
+
+    test('handles null method channel response', () async {
+      stubPlatform.addResponse(name: queryMethodName, value: null);
+
+      final SkuDetailsResponseWrapper response = await billingClient
+          .querySkuDetails(
+              skuType: SkuType.inapp, skusList: <String>['invalid']);
+
+      BillingResultWrapper billingResult = BillingResultWrapper(
+          responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage);
+      expect(response.billingResult, equals(billingResult));
+      expect(response.skuDetailsList, isEmpty);
+    });
   });
 
   group('launchBillingFlow', () {
@@ -197,6 +223,18 @@ void main() {
       expect(arguments['sku'], equals(skuDetails.sku));
       expect(arguments['accountId'], isNull);
     });
+
+    test('handles method channel returning null', () async {
+      stubPlatform.addResponse(
+        name: launchMethodName,
+        value: null,
+      );
+      final SkuDetailsWrapper skuDetails = dummySkuDetails;
+      expect(
+          await billingClient.launchBillingFlow(sku: skuDetails.sku),
+          equals(BillingResultWrapper(
+          responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+    });
   });
 
   group('queryPurchases', () {
@@ -247,6 +285,19 @@ void main() {
       expect(response.responseCode, equals(expectedCode));
       expect(response.purchasesList, isEmpty);
     });
+
+    test('handles method channel returning null', () async {
+      stubPlatform.addResponse(
+        name: queryPurchasesMethodName,
+        value: null,
+      );
+      final PurchasesResultWrapper response =
+          await billingClient.queryPurchases(SkuType.inapp);
+
+      expect(response.billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+      expect(response.responseCode, BillingResponse.error);
+      expect(response.purchasesList, isEmpty);
+    });
   });
 
   group('queryPurchaseHistory', () {
@@ -294,6 +345,18 @@ void main() {
       expect(response.billingResult, equals(expectedBillingResult));
       expect(response.purchaseHistoryRecordList, isEmpty);
     });
+
+    test('handles method channel returning null', () async {
+      stubPlatform.addResponse(
+        name: queryPurchaseHistoryMethodName,
+        value: null,
+      );
+      final PurchasesHistoryResult response =
+          await billingClient.queryPurchaseHistory(SkuType.inapp);
+
+      expect(response.billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+      expect(response.purchaseHistoryRecordList, isEmpty);
+    });
   });
 
   group('consume purchases', () {
@@ -313,6 +376,17 @@ void main() {
 
       expect(billingResult, equals(expectedBillingResult));
     });
+
+    test('handles method channel returning null', () async {
+      stubPlatform.addResponse(
+        name: consumeMethodName,
+        value: null,
+      );
+      final BillingResultWrapper billingResult = await billingClient
+          .consumeAsync('dummy token', developerPayload: 'dummy payload');
+
+      expect(billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+    });
   });
 
   group('acknowledge purchases', () {
@@ -333,5 +407,16 @@ void main() {
 
       expect(billingResult, equals(expectedBillingResult));
     });
+    test('handles method channel returning null', () async {
+      stubPlatform.addResponse(
+        name: acknowledgeMethodName,
+        value: null,
+      );
+      final BillingResultWrapper billingResult =
+          await billingClient.acknowledgePurchase('dummy token',
+              developerPayload: 'dummy payload');
+
+      expect(billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+    });
   });
 }

packages/in_app_purchase/test/billing_client_wrappers/purchase_wrapper_test.dart

@@ -112,6 +112,14 @@ void main() {
       expect(parsed.responseCode, equals(expected.responseCode));
       expect(parsed.purchasesList, containsAll(expected.purchasesList));
     });
+
+    test('parsed from empty map', () {
+      final PurchasesResultWrapper parsed =
+          PurchasesResultWrapper.fromJson(<String, dynamic>{});
+      expect(parsed.billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+      expect(parsed.responseCode, BillingResponse.error);
+      expect(parsed.purchasesList, isEmpty);
+    });
   });
 
   group('PurchasesHistoryResult', () {
@@ -140,6 +148,13 @@ void main() {
       expect(parsed.purchaseHistoryRecordList,
           containsAll(expected.purchaseHistoryRecordList));
     });
+
+    test('parsed from empty map', () {
+      final PurchasesHistoryResult parsed =
+          PurchasesHistoryResult.fromJson(<String, dynamic>{});
+      expect(parsed.billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+      expect(parsed.purchaseHistoryRecordList, isEmpty);
+    });
   });
 }
 

packages/in_app_purchase/test/billing_client_wrappers/sku_details_wrapper_test.dart

@@ -99,6 +99,27 @@ void main() {
       expect(parsed.billingResult, equals(expected.billingResult));
       expect(parsed.skuDetailsList, containsAll(expected.skuDetailsList));
     });
+
+    test('fromJson creates an object with default values', (){
+      final SkuDetailsResponseWrapper skuDetails =
+          SkuDetailsResponseWrapper.fromJson(<String, dynamic>{});
+      expect(skuDetails.billingResult, equals(BillingResultWrapper(responseCode: BillingResponse.error, debugMessage: kInvalidBillingResultErrorMessage)));
+      expect(skuDetails.skuDetailsList, isEmpty);
+    });
+  });
+
+  group('BillingResultWrapper', () {
+    test('fromJson on empty map creates an object with default values', (){
+      final BillingResultWrapper billingResult = BillingResultWrapper.fromJson(<String, dynamic>{});
+      expect(billingResult.debugMessage, kInvalidBillingResultErrorMessage);
+      expect(billingResult.responseCode, BillingResponse.error);
+    });
+
+    test('fromJson on null creates an object with default values', (){
+      final BillingResultWrapper billingResult = BillingResultWrapper.fromJson(null);
+      expect(billingResult.debugMessage, kInvalidBillingResultErrorMessage);
+      expect(billingResult.responseCode, BillingResponse.error);
+    });
   });
 }
 

packages/in_app_purchase/test/store_kit_wrappers/sk_methodchannel_apis_test.dart

@@ -20,6 +20,10 @@ void main() {
 
   setUp(() {});
 
+  tearDown(() {
+    fakeIOSPlatform.testReturnNull = false;
+  });
+
   group('sk_request_maker', () {
     test('get products method channel', () async {
       SkProductResponseWrapper productResponseWrapper =
@@ -84,6 +88,11 @@ void main() {
       expect(await SKPaymentQueueWrapper.canMakePayments(), true);
     });
 
+    test('canMakePayment returns false if method channel returns null', () async {
+      fakeIOSPlatform.testReturnNull = true;
+      expect(await SKPaymentQueueWrapper.canMakePayments(), false);
+    });
+
     test('transactions should return a valid list of transactions', () async {
       expect(await SKPaymentQueueWrapper().transactions(), isNotEmpty);
     });
@@ -132,6 +141,7 @@ class FakeIOSPlatform {
   // get product request
   List<dynamic> startProductRequestParam = [];
   bool getProductRequestFailTest = false;
+  bool testReturnNull = false;
 
   // refresh receipt request
   int refreshReceipt = 0;
@@ -165,6 +175,9 @@ class FakeIOSPlatform {
         return Future<String>.value('receipt data');
       // payment queue
       case '-[SKPaymentQueue canMakePayments:]':
+        if (testReturnNull) {
+          return Future<dynamic>.value(null);
+        }
         return Future<bool>.value(true);
       case '-[SKPaymentQueue transactions]':
         return Future<List<dynamic>>.value(