PHP Fatal error

Hello,

thanks for a great plugin, I use it for year, but now I just found scenario where it’s not working

I want WP to delete all connected attachments when post is deleted, so I use:

add_action( 'before_delete_post', 'maybe_delete_post_attachments', 10, 1 );
function maybe_delete_post_attachments( $post_id ){
	if( get_post_type( $post_id ) == 'inzerat' ){
		$attachments = get_attached_media( '', $post_id );
		foreach( $attachments as $attachment ){
			wp_delete_attachment( $attachment->ID, 'true' );
		}
	}
}

but it’s not working because of Fly Dynamic Image Resizer:

PHP Fatal error:  Uncaught Error: Call to undefined function JB\FlyImages\WP_Filesystem() in /wp-content/plugins/fly-dynamic-image-resizer/inc/class-core.php:114
Stack trace:
#0 /wp-includes/class-wp-hook.php(289): JB\FlyImages\Core->delete_attachment_fly_images(374)
#1 /wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#2 /wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#3 /wp-includes/post.php(5940): do_action('delete_attachme...', 374, Object(WP_Post))
#4 /wp-content/themes/xxx/functions.php(1020): wp_delete_attachment(374, 'true')
#5 /wp-includes/class-wp-hook.php(289): maybe_delete_post_attachments(373)
#6 /wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#7 /wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#8 /wp-includes/post.php(3038): do_action('before_delete_p...', 373, Object(WP_Post))
#9 /wp-content/themes/xxx/functions.php(1009): wp_delete_post(373, true)
#10 /wp-includes/class-wp-hook.php(287): get_delete_old_posts()
#11 /wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters('', Array)
#12 /wp-includes/plugin.php(551): WP_Hook->do_action(Array)
#13 /wp-cron.php(138): do_action_ref_array('delete_old_post...', Array)
#14 {main}