Force users to log out when booking

<?php
/**
 * Force users to log out before booking
 * @param boolean $result
 * @param EM_Booking $EM_Booking
 * @return boolean
 */
function my_em_booking_force_guests($result, $EM_Booking){
    if( is_user_logged_in() ){
        $EM_Booking->add_error('Please log out to make a booking.');
        return false;
    }
    return $result;
}
add_filter('em_booking_validate','my_em_booking_force_guests', 1, 2);