Fix warning notice related to subscriptions helper (#4020)

* Fix warning notice related to the new subscriptions helper

* Checking for an empty value instead

* Changelog and readme entries

Author: wjrosa

changelog.txt

@@ -1,6 +1,7 @@
 *** Changelog ***
 
 = 9.3.0 - xxxx-xx-xx =
+* Fix - Improves the checking for existing customer attribute when retrieving a payment method that may be detached from a subscription.
 * Fix - Reverts the default value for the `capture_method` property to avoid breaking Amazon Pay when creating a payment intent.
 * Add - Adds a new feature flag to handle the Single Payment Element feature.
 * Dev - Moves the method to check if the subscriptions extension is enabled to a new helper class.

includes/compat/class-wc-stripe-subscriptions-helper.php

@@ -48,7 +48,7 @@ public static function get_detached_subscriptions() {
 			$source_id = $subscription->get_meta( '_stripe_source_id' );
 			if ( $source_id ) {
 				$payment_method = WC_Stripe_API::get_payment_method( $source_id );
-				if ( ! $payment_method->customer ) {
+				if ( empty( $payment_method->customer ) ) {
 					$detached_subscriptions[] = [
 						'id'                        => $subscription->get_id(),
 						'customer_id'               => $subscription->get_meta( '_stripe_customer_id' ),

readme.txt

@@ -111,6 +111,7 @@ If you get stuck, you can ask for help in the [Plugin Forum](https://wordpress.o
 == Changelog ==
 
 = 9.3.0 - xxxx-xx-xx =
+* Fix - Improves the checking for existing customer attribute when retrieving a payment method that may be detached from a subscription.
 * Fix - Reverts the default value for the `capture_method` property to avoid breaking Amazon Pay when creating a payment intent.
 * Add - Adds a new feature flag to handle the Single Payment Element feature.
 * Dev - Moves the method to check if the subscriptions extension is enabled to a new helper class.