Get and use logged in username variable in menu

function kleo_bp_replace_placeholders_extra( $output, $initial_output ) {
    if ( strpos( $output, '##username##' ) !== false ) {
        if ( ! is_user_logged_in() ) {
            return '';
        }
        $current_user = wp_get_current_user();
        $username = $current_user->user_login;
        $output = str_replace('##username##', $username, $output);
    }
    return $output;
}

add_filter('walker_nav_menu_start_el', 'kleo_bp_replace_placeholders_extra');