+ if (is_null($participate)) {
+ unsubscribe($participant_list, $email);
+ subscribe($absent_list, $email);
+ } elseif ($participate) {
+ subscribe($participant_list, $email);
+ unsubscribe($absent_list, $email);
+ } else {
+ unsubscribe($participant_list, $email);
+ unsubscribe($absent_list, $email);
+ }