Passing null to parameter error

Hi, i have deprecated warning with your plugin in PHP version 8.2.11

Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated in ...\wp-includes\functions.php on line?7127

It’s because of bad calling of add_submenu_page in public function add_page() {

Sollution is to set first parameter to blank string rather than null

add_submenu_page( null, 'Add Client', 'Add Client', 'manage_options', 'wo_add_client', 'wo_add_client_page' );
add_submenu_page( null, 'Edit Client', 'Edit Clients', 'manage_options', 'wo_edit_client', 'wo_admin_edit_client_page' );