Bug when trying to create a sale.contract.line

Hi vivek, when I try to create a new sale.contract.line

  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/netsvc.py", line 489, in dispatch
    result = ExportService.getService(service_name).dispatch(method, auth, params)
  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/service/web_services.py", line 599, in dispatch
    res = fn(db, uid, *params)
  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/osv/osv.py", line 122, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/osv/osv.py", line 176, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/osv/osv.py", line 167, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/addons/commission_ava/sale_contract.py", line 266, in write
    self.update_price(cr, uid, ids, context=context)
  File "/home/openerp_user/openerp/openerp_V6_stable/server/bin/addons/commission_ava/sale_contract.py", line 48, in update_price
    age=datetime.strptime(data['effect_date'],'%Y-%m-%d')-datetime.strptime(line.traveller_id.birthdate,'%Y-%m-%d')
TypeError: strptime() argument 1 must be string, not bool

The first time I forget to specify the effect date and the birthdate, but even after specify them, I still get the error.