[16.x] Return PaymentMethod when already default; accept StripePaymentMethod instance

- Avoid returning null from updateDefaultPaymentMethod when the provided
  payment method is already the customer's default (return a PaymentMethod
  instance instead).
- Accept Stripe\\PaymentMethod instances directly to avoid an extra retrieval.
- Updated test_we_can_set_a_default_payment_method to exercise the "already
  default" path.

Author: gurindersingh

src/Concerns/ManagesPaymentMethods.php

@@ -171,13 +171,16 @@ public function updateDefaultPaymentMethod(StripePaymentMethod|string $paymentMe
 
         $customer = $this->asStripeCustomer();
 
-        $stripePaymentMethod = $this->resolveStripePaymentMethod($paymentMethod);
+        $stripePaymentMethod = $paymentMethod instanceof StripePaymentMethod
+            ? $paymentMethod
+            : $this->resolveStripePaymentMethod($paymentMethod);
 
         // If the customer already has the payment method as their default, we can bail out
         // of the call now. We don't need to keep adding the same payment method to this
         // model's account every single time we go through this specific process call.
+        // We will return current PaymentMethod set in invoice settings
         if ($stripePaymentMethod->id === $customer->invoice_settings->default_payment_method) {
-            return null;
+            return new PaymentMethod($this, $stripePaymentMethod);
         }
 
         $paymentMethod = $this->addPaymentMethod($stripePaymentMethod);

tests/Feature/PaymentMethodsTest.php

@@ -118,6 +118,13 @@ public function test_we_can_set_a_default_payment_method()
         $this->assertEquals('4242', $paymentMethod->card->last4);
         $this->assertTrue($user->hasDefaultPaymentMethod());
 
+        $paymentMethod = $user->updateDefaultPaymentMethod($paymentMethod->asStripePaymentMethod());
+
+        $this->assertInstanceOf(PaymentMethod::class, $paymentMethod);
+        $this->assertEquals('visa', $paymentMethod->card->brand);
+        $this->assertEquals('4242', $paymentMethod->card->last4);
+        $this->assertTrue($user->hasDefaultPaymentMethod());
+
         $paymentMethod = $user->defaultPaymentMethod();
 
         $this->assertInstanceOf(PaymentMethod::class, $paymentMethod);