PHP - symfony2 - Getting error when checking whether Session is set or not -

problem - want check whether session set or not in '__construct' of 'controller', getting following error -

fatalerrorexception: compile error: cannot use isset() on result of function call (you can use "null !== func()" instead)

the following code snippet in '__construct' -

function __construct() {     $request = request::createfromglobals();    $session = $request->getsession();    if(!isset($session->get('id'))){      $this->redirect('userauthbundle:auth:login.html.twig');    }  } 

if use '!= null' instead of '!isset' giving me error following -

fatalerrorexception: error: call member function get() on non-object

is there other alternative way can implemented.

thanks in advance.

manual says:

warning

isset() works variables passing else result in parse error. checking if constants set use defined() function.