[Koha-devel] need help in expiry date

Hi, I am using koha 2.2.9 and I want to know is there any check on expiry date and joining date when adding a patron. I find out that user(admin) can save expiry date less then the joining date. there should be a check of date to restict the user to add the expiry date not less then the joining date. If a user add the date of joining "12/02/2008"then the expiry date should be greater or equal to the joining date. If any body has done this please forward. Regards, Zahid