the explicit nullable type must be used in php 8.4

[mouson]

PHP 8.4
Wordpress 6.9
Plugin mailgun 2.1.10

Error message:

Deprecated: mg_api_last_error(): Implicitly marking parameter $error as nullable is deprecated, the explicit nullable type must be used instead in /wp-content/plugins/mailgun/includes/wp-mail-api.php on line 36

Deprecated: mg_dump_headers(): Implicitly marking parameter $headers as nullable is deprecated, the explicit nullable type must be used instead in /wp-content/plugins/mailgun/includes/mg-filter.php on line 259

[mshcherb]

@mouson Thanks for reporting this issue!
made fix in this pr