JUser::_load:Unable to load user with id 1

$user_id = $ticket->getUserId();
$user =& JFactory::getUser($user_id);

$table   = JUser::getTable();
$user_id = intval( $ticket->getUserId() );

if($table->load( $user_id ))
{
         $user =& JFactory::getUser($user_id);
         // now you are sure user exists
} else {
         // user doesn't exists
}