Runtime Deprecated code usage!

Fuel\Core\PhpErrorException [ Runtime Deprecated code usage ]: json_decode(): Passing null to parameter #1 ($json) of type string is deprecated

COREPATH/classes/controller.php @ line 65:

64:	$perfil = \Auth::get("perfil");
65:	Session::set('privilegios',json_decode(\Auth::get('privilegios'), true));
66:	$reporte = array();