Error Message

[Bruce1952]

Server Info:

Server OS: Linux 4.18.0-553.27.1.lve.el8.x86_64
Server Date: 26/01/2025 23:23:54
Server Up Time: Disabled/Unavailable
HTTP Server: Apache
PHP Version: 8.1.31 (Zend: 4.1.31)
PHP File Uploads: On
Upload Max Size: 1024M
PHP Memory Limit: -1
POST Max Size: 1024M
Database Engine: MySQL 10.6.20-MariaDB-cll-lve
Database Host: localhost (xxxx)
Database Date: 26/01/2025 23:23:54
Database Data Size: 434,469 kB
Database Index Size: 95,651 kB
MySQL Slow Query Log Status: Off
MySQL Slow Query Log File: xxxl494161-slow.log
MySQL Mode: NO_ENGINE_SUBSTITUTION

I am getting this error message:
[26-Jan-2025 12:35:54 Australia/Sydney] Request URI: /index.php?main_page=addon_reviews_reminder_optout, IP address: 220.244.78.72, Language id 1
#0 /includes/modules/pages/addon_reviews_reminder_optout/header_php.php(10): zen_debug_error_handler()
#1 /index.php(35): require('/home/...')
--> PHP Warning: Undefined array key "customer_id" in /includes/modules/pages/addon_reviews_reminder_optout/header_php.php on line 10.

This is what is in the file:

if (!$_SESSION['customer_id']) {
$_SESSION['navigation']->set_snapshot();
zen_redirect(zen_href_link(FILENAME_LOGIN, '', 'SSL'));
}

require(DIR_WS_MODULES . zen_get_module_directory('require_languages.php'));
$breadcrumb->add(NAVBAR_TITLE);

#PROCESS OPT OUT REQUEST
if( isset($_POST['optOutToken']) and $_POST['optOutToken'] == md5( (int)$_SESSION['customer_id'] * 5 ) ){
$sql = "INSERT IGNORE INTO `" . TABLE_ADDON_REVIEW_REMINDER_OPTOUT . "` (`customers_id`, `date_time`)
VALUES ('" . zen_db_prepare_input( (int)$_SESSION['customer_id'] ) . "','" . date("Y-m-d H:i:s") . "')";
$db->Execute($sql);
}
?>

Can anyone tell me what I need to change to correct the error message please.

[mc12345678]

What have to do and what might make sense in review of just the problem area:
Changing:

if (!$_SESSION['customer_id']) {

To at least:

if (empty($_SESSION['customer_id'])) {

Considering using Zen Cart 1.5.8, there is now also a function that checks for being logged in and allows for the possibility of accessing something by not actually having an account but having been "logged in".

Would have to review for more detail about whether those type customers should even be allowed to continue in that file.

The above though will basically follow the same action as previous for users that have created an account.