Summary

Fixes #2283: The initCustomerSheet method has a misleading return type.

Problem

• Return type was Future<CustomerSheetResult?> suggesting payment data might be returned
• Actual behavior: always returns null on success, throws exception on error
• Doesn't match React Native SDK which uses Promise<{ error?: StripeError }>

Solution

• Change return type to Future<void>
• Simplify implementation to only check for errors
• Add doc comment clarifying it throws StripeException on failure

Changes

• stripe_platform_interface.dart - Updated interface signature
• method_channel_stripe.dart - Simplified implementation
• stripe.dart - Updated public facade
• web_stripe.dart - Updated web implementation

Breaking Change

This is a minor breaking change for any code that was capturing the (always null) return value. The fix is simple - just remove the variable assignment since the method now returns void.

Before:

final result = await Stripe.instance.initCustomerSheet(...); // result always null

After:

await Stripe.instance.initCustomerSheet(...);

Test plan

• All existing tests pass (25/25 method channel tests)
• Manual verification on iOS
• Manual verification on Android