PHP code deprecated - Urgent fix

We have some issues in our side due to PHP version upgrade on Godaddy. There are some variables not availble anymore. Below is the error log and code snippet.

[16-Jul-2021 02:24:28 UTC] PHP Notice: Undefined index: QUERY_STRING in /home/vvl7qkzmhhyd/public_html/login/call_ub_embed.php on line 65
[16-Jul-2021 02:24:28 UTC] PHP Notice: Undefined variable: custqs in /home/vvl7qkzmhhyd/public_html/login/call_ub_embed.php on line 66

$qs = $_ENV['QUERY_STRING'] ? $_ENV['QUERY_STRING'] : $_SERVER['QUERY_STRING'];
if($custqs) { $qs .= $qs ? "&" : ""; $qs .= $custqs; }