error shown in apache2 related to track.php

[AFA]

Hi,

I am getting an error in the Apache2 error log file:

[Thu Sep 14 11:04:19.246012 2023] [php7:notice] [pid 7525] [client 103.59.198.110:54533] 

PHP Notice:  Undefined index: in_tab in /var/www/html/sp/subjects/track.php on line 56, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=SCC
[Thu Sep 14 11:04:19.246056 2023] [php7:notice] [pid 7525] [client 103.59.198.110:54533] PHP Notice:  Undefined index: in_pluslet in /var/www/html/sp/subjects/track.php on line 57, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=SCC
[Thu Sep 14 11:05:08.693082 2023] [php7:notice] [pid 7526] [client 103.59.198.110:54587] PHP Notice:  Undefined index: in_tab in /var/www/html/sp/subjects/track.php on line 56, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=LexisAdvance
[Thu Sep 14 11:05:08.693127 2023] [php7:notice] [pid 7526] [client 103.59.198.110:54587] PHP Notice:  Undefined index: in_pluslet in /var/www/html/sp/subjects/track.php on line 57, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=LexisAdvance
[Thu Sep 14 11:05:15.096698 2023] [php7:notice] [pid 7534] [client 220.158.168.35:54590] PHP Notice:  Undefined index: in_tab in /var/www/html/sp/subjects/track.php on line 56, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=LexisAdvance
[Thu Sep 14 11:05:15.096737 2023] [php7:notice] [pid 7534] [client 220.158.168.35:54590] PHP Notice:  Undefined index: in_pluslet in /var/www/html/sp/subjects/track.php on line 57, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=LexisAdvance
[Thu Sep 14 11:05:33.975001 2023] [php7:notice] [pid 7530] [client 103.59.198.110:54595] PHP Notice:  Undefined index: in_tab in /var/www/html/sp/subjects/track.php on line 56, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=LexisAdvance
[Thu Sep 14 11:05:33.975078 2023] [php7:notice] [pid 7530] [client 103.59.198.110:54595] PHP Notice:  Undefined index: in_pluslet in /var/www/html/sp/subjects/track.php on line 57, referer: https://libguides.jgu.edu.in/subjects/guide.php?subject=LexisAdvance



Here is the track.php file:
<?php
use SubjectsPlus\Control\Querier;
use SubjectsPlus\Control\Stats\Stats;

header('Content-Type: image/gif');
header("Cache-Control: private, no-cache, no-cache=Set-Cookie, proxy-revalidate");
header("Expires: Wed, 11 Jan 2000 12:59:00 GMT");
header("Last-Modified: Wed, 11 Jan 2006 12:59:00 GMT");
header("Pragma: no-cache");

echo base64_decode('R0lGODlhAQABAJAAAP8AAAAAACH5BAUQAAAALAAAAAABAAEAAAICBAEAOw==');

include("../control/includes/config.php");
include("../control/includes/functions.php");
include("../control/includes/autoloader.php");

$db = new Querier;
$stats = new Stats($db);

if(isset($_SERVER['HTTP_REFERER'])) {
$stats->setHttpReferer($_SERVER['HTTP_REFERER']);
} else {
$stats->setHttpReferer("Referer Unavailable");
}

if(isset($_SERVER['REMOTE_ADDR'])) {
$stats->setRemoteAddress($_SERVER['REMOTE_ADDR']);
}

if(isset($_GET['page_title'])) {
$stats->setPageTitle($_GET['page_title']);
}

if(isset($_SERVER['HTTP_USER_AGENT'])) {
$stats->setUserAgent($_SERVER['HTTP_USER_AGENT']);
}

if(isset($_GET['subject'])) {
$stats->setSubjectShortForm($_GET['subject']);
}

if(isset($_GET['event_type'])) {
$stats->setEventType($_GET['event_type']);
} else {
$stats->setEventType("view");

}

if(isset($_GET['tab_name'])) {
$stats->setTabName($_GET['tab_name']);
}

if(isset($_GET['link_url'])) {
$stats->setLinkUrl($_GET['link_url']);
$stats->setLinkTitle($_GET['link_title']);
$stats->setInTab($_GET['in_tab']);
$stats->setInPluslet($_GET['in_pluslet']);
}

$stats->saveStats();