HTML Validator crashes in 2.0.1

Problem is in the is_mobile function of framework/core/subsystems/expTheme.php:

HTTP_ACCEPT could possibly be not set so have to change it to the following:

    if (isset($_SERVER['HTTP_ACCEPT']) && (strpos(strtolower($_SERVER['HTTP_ACCEPT']),'application/vnd.wap.xhtml+xml') > 0) or ((isset($_SERVER['HTTP_X_WAP_PROFILE']) or isset($_SERVER['HTTP_PROFILE'])))) {
        $mobile_browser++;
    }