It was very nice but today it crashed my site

Hi there,

I really loved your plugin but after installing WP 6.0 (PHP 7.4, WPML and TOTAL theme as Template) it crashed my site.

Something caued a 500 error -> post-page-specific-custom-css.php on line 519

This is the debug information (XXXX for security reason):

[01-Jul-2022 11:48:39 UTC] PHP Fatal error:  Uncaught TypeError: Argument 1 passed to Phylax\WPPlugin\PPCustomCSS\Plugin::the_content() must be of the type string, null given, called in /XXXXXXXXXXXXX/wordpress/wp-includes/class-wp-hook.php on line 307 and defined in /XXXXXXXXXXXXX/wordpress/wp-content/plugins/postpage-specific-custom-css/post-page-specific-custom-css.php:519
Stack trace:
#0 /XXXXXXXXXXXXX/wordpress/wp-includes/class-wp-hook.php(307): Phylax\WPPlugin\PPCustomCSS\Plugin->the_content(NULL)
#1 /XXXXXXXXXXXXX/wordpress/wp-includes/plugin.php(191): WP_Hook->apply_filters(NULL, Array)
#2 /XXXXXXXXXXXXX/wordpress/wp-includes/formatting.php(3877): apply_filters('the_content', '')
#3 /XXXXXXXXXXXXX/wordpress/wp-includes/class-wp-hook.php(307): wp_trim_excerpt('', Object(WP_Post))
#4 /XXXXXXXXXXXXX/wordpress/wp-includes/plugin.php(191): WP_Hook->apply_filters('', Array)
#5 /XXXXXXXXXXXXX/wordpress/wp-includes/post-templa in /XXXXXXXXXXXXX/wordpress/wp-content/plugins/postpage-specific-custom-css/post-page-specific-custom-css.php on line 519

Any ideas?