System throws an error when evaluating life events

We have a requirement where , for a plan coverage amount is calculated based on the hours worked in the previous year. Employees who have worked less than 702 hours should be getting 0% coverage. We have a fast formula to calculate this and when we evaluate life events for such employees, system throws the below error instead of assigning 0%. If I update the FF logic to return 0.1 instead of 0 then this works. Has anyone faced this issue before? Is there any workaround to assign 0% coverage without getting any error?

Thanks,

Diya