Deprecation fix: PHP 8.4: Implicitly nullable parameter declarations deprecated

[GityaMan]

Hi! Please fix the deprecation in the package.

PHP Deprecated: Paymentwall_Product::__construct(): Implicitly marking parameter $trialProduct as nullable is deprecated, the explicit nullable type must be used instead in /var/www/vendor/paymentwall/paymentwall-php/lib/Paymentwall/Product.php on line 23

You can use the rule nullable_type_declaration_for_default_null_value for PhpCsFixer.

[SPie]

Fixing this might be an issue since the package supports PHP >= 5.2, and nullable types for function parameters were added with PHP 7.1.
To fix the deprecation, the package would have to branch into two supported versions: one for PHP < 8.4 and one for PHP >= 7.1, where the deprecation can be fixed.