Hii,
I would use isset and empty:
session_start();
if(isset($_SESSION['blah']) && !empty($_SESSION['blah'])) {
echo 'Set and not empty, and no undefined index error!';
}
array_key_exists is a nice alternative to using isset to check for keys:
session_start();
if(array_key_exists('blah',$_SESSION) && !empty($_SESSION['blah'])) {
echo 'Set and not empty, and no undefined index error!';
}
Make sure you're calling session_start before reading from or writing to the session array.
Hope it helps!!