Cron for clean user_http_session

[happyfredo]

Hi,

Is there a way to clean user_http_session .
Actually i notice that this table is not clear, and when i have notification i don't receive email because of
/protected/humhub/modules/notification/Module.php

$isOnline = (count($user->httpSessions) > 0);
When my session is expire, the entry in table stay, so i don't receive mail.

Best regards