How to solve undefined index error

How to solve undefined index error

if(isset($_SESSION['evt_year'])
|| isset($_SESSION['evt_title'])
|| isset($_SESSION['evt_sdate'])
|| isset($_SESSION['evt_place'])
|| isset($_SESSION['evt_stime'])
|| isset($_SESSION['evt_etime'])
|| isset($_SESSION['evt_desc'])) {
$output.=$_GET['title']; //the error is here
}
else {
$output.="";
}
Notice the error I got:
Undefined index: title in
C:\xampp\htdocs\ICT\abc\cal1\EventCalender\classes\EventRecordForm.php on
line 13