Undefined index in cron_runner

hi,

in my debug log, I can see that

{17190:Wed, 24 Jan 2018 01:35:07 GMT} Zenphoto v1.4.14
NOTICE: Undefined index: link in /home/avbo7291/public_html/zenphoto/zp-core/cron_runner.php on line 16
{26594:Sun, 28 Jan 2018 22:21:34 GMT}
NOTICE: Undefined index: link in /home/avbo7291/public_html/zenphoto/zp-core/cron_runner.php on line 16

and in the same time I can see in my security log:

2018-01-24 02:35:07     65.55.210.73    Admin access            Failed      /zp-core/cron_runner.php
2018-01-28 23:21:34     199.30.24.102   Admin access            Failed      /zp-core/cron_runner.php

any explanations of that log?

in fact, in actual code of cron_runner.php, I can see (1st line is line 16):

[...]
$link = sanitize($_POST['link']);
if (isset($_POST['auth'])) {
    $auth = sanitize($_POST['auth']);
    $admin = $_zp_authority->getMasterUser();
    if (sha1($link . serialize($admin)) == $auth && $admin->getRights()) {
        $_zp_current_admin_obj = $admin;
        $_zp_loggedin = $admin->getRights();
    }
}

and there is no test if $_POST['link'] is set or not