How can we do rule wise exception handling in the drools rule condition? My scenario is how to handle scenarios when the schema of an event changes.

For example, let's say Initially I have an event that has 5 members namely name,num1,num2,num3,num4. I started creating rules for the event and the rule engine is running for some time. After that let's assume there is a scenario in which one of the class members (say num4) is removed from the event because of some reason. Now what I can do now is to change the Event class, but all the rules associated with that member will give me exceptions. The exceptions will also affect other rules which can run with the current data. Is there any way to handle exception in rule condition for specific rule and restrict it to disturb the independent rules.