Warning: strpos(): Empty needle in ……wordpress Plugin

I get this error :

Warning: strpos(): Empty needle in ……popularity-contest.php on line 2574

function akpc_is_searcher() {
        global $akpc;
        $referrer = parse_url($_SERVER['HTTP_REFERER']);
        $searchers = explode(' ', preg_replace("\n|\r|\r\n|\n\r", ' ', $akpc->searcher_names));
        foreach ($searchers as $searcher) {
                if (strpos($referrer['host'], $searcher) !== false) {
                        return true;
                }
        }
        return false;
}

Can someone please help me to fix this problem?