Implicitly marking parameters as nullable is deprecated, the explicit nullable type must be used instead

[andyexeter]

Since PHP 8.4, it is now deprecated to not mark parameters as explicitly nullable: https://wiki.php.net/rfc/deprecate-implicitly-nullable-types

There are a number of places in this library that need updating to fix these deprecations. For example, this:

cybersource-rest-client-php/lib/ApiClient.php

Line 105 in 39d1fbd

public function __construct(\CyberSource\Configuration $config = null, \CyberSource\Authentication\Core\MerchantConfiguration $merchantConfig = null)

Needs to be updated to:

public function __construct(?\CyberSource\Configuration $config = null, ?\CyberSource\Authentication\Core\MerchantConfiguration $merchantConfig = null)