getDefaultPaymentMethod() sometimes throws an error

[prattcmp]

Cashier Stripe Version

15.6.0

Laravel Version

11.5.0

PHP Version

8.1.0

Database Driver & Version

No response

Description

When we call the defaultPaymentMethod() method for certain users, we get a Attempt to read property "default_payment_method" on null exception triggered in /vendor/laravel/cashier/src/Concerns/ManagesPaymentMethods.php on this if statement even though the customer has a valid subscription and Stripe ID:

if ($customer->invoice_settings->default_payment_method) {
    return new PaymentMethod($this, $customer->invoice_settings->default_payment_method);
}

We believe this may be happening because the customer has a 100% off coupon and therefore wasn't required to enter a payment method when creating their subscription using Stripe Checkout. We create all new subscriptions with Stripe Checkout using this method:

return $user
            ->newSubscription(config('cashier.subscriptions.monthly'), $validated['interval'] == 'annual' ? $plan['yearly_price_id'] : $plan['monthly_price_id'])
            ->quantity($validated['quantity'])
            ->checkout([
                'success_url' => route('billing.show').'?'.$new_user_query_string.'session_id={CHECKOUT_SESSION_ID}',
                'cancel_url' => route('billing.show'),
                'allow_promotion_codes' => true,
                'tax_id_collection' => [
                    'enabled' => true,
                ],
            ]);

Steps To Reproduce

1. Create a subscription using Stripe Checkout and use a 100% off coupon code.
2. Call $user->defaultPaymentMethod().

[driesvints]

Thanks for your report. This should actually never happen because invoice_settings is always an associative array according to the Stripe API docs: https://docs.stripe.com/api/customers/object#customer_object-invoice_settings. It should never be null.

Regardless, we should protect against it so it doesn't fails over in Cashier.

But if you can, could you submit this as a support question to Stripe so they can look into it?