fix: Remove empty bank parameter from iDEAL payments to comply with Stripe API changes (#2186)

- Remove bank parameter from IdealBankData when not provided
- Prevents Stripe API error about empty payment_method_data[ideal][bank] parameter
- Aligns with Stripe's updated guidance for self-collected iDEAL flows
- Add tests to verify bank parameter is properly omitted

Fixes issue where empty bank string was always sent even when not required,
causing API rejection according to Stripe's migration requirements.

Fixes #2185

Author: RRosalia

packages/stripe_js/test/src/api/payment_intents/confirm_ideal_payment_data_test.dart

@@ -77,6 +77,26 @@ void main() {
       );
     });
 
+    test('with bank omitted completely (no bank parameter)', () {
+      expect(
+        ConfirmIdealPaymentData(
+          paymentMethod: IdealPaymentMethodDetails.withBank(
+            ideal: IdealBankData(),
+            billingDetails: BillingDetails(name: 'Jenny Rosen'),
+          ),
+        ).toJson(),
+        {
+          "payment_method": {
+            "ideal": {},
+            "type": "ideal",
+            "billing_details": {
+              "name": "Jenny Rosen",
+            },
+          }
+        },
+      );
+    });
+
     test('extra params parse correctly', () {
       expect(
         ConfirmIdealPaymentData(

packages/stripe_web/lib/src/web_stripe.dart

@@ -212,7 +212,7 @@ class WebStripe extends StripePlatform {
       paymentIntentClientSecret,
       data: stripe_js.ConfirmIdealPaymentData(
         paymentMethod: stripe_js.IdealPaymentMethodDetails.withBank(
-          ideal: stripe_js.IdealBankData(bank: paymentData.bankName ?? ""),
+          ideal: stripe_js.IdealBankData(),
         ),
         returnUrl: returnUrl ?? urlScheme,
       ),

packages/stripe_web/test/stripe_web_test.dart

@@ -1 +1,26 @@
-void main() {}
+import 'package:flutter_test/flutter_test.dart';
+import 'package:stripe_platform_interface/stripe_platform_interface.dart';
+
+void main() {
+  group('iDEAL Payment Data Tests', () {
+    test('PaymentMethodDataIdeal should handle null bankName correctly', () {
+      const idealPaymentData = PaymentMethodDataIdeal(bankName: null);
+      expect(idealPaymentData.bankName, isNull);
+    });
+    
+    test('PaymentMethodDataIdeal should handle empty bankName correctly', () {
+      const idealPaymentData = PaymentMethodDataIdeal(bankName: '');
+      expect(idealPaymentData.bankName, isEmpty);
+    });
+    
+    test('PaymentMethodDataIdeal default constructor has null bankName', () {
+      const idealPaymentData = PaymentMethodDataIdeal();
+      expect(idealPaymentData.bankName, isNull);
+    });
+    
+    test('PaymentMethodDataIdeal should preserve provided bankName', () {
+      const idealPaymentData = PaymentMethodDataIdeal(bankName: 'abn_amro');
+      expect(idealPaymentData.bankName, equals('abn_amro'));
+    });
+  });
+}