Abs% Error Expression Not Returning Value

Summary:

We created a custom measure to calculate the Abs% Error, but we cannot get it to return a value.

The expression uses Booking History, and Booking Forecast to derive the %. This issue is when there is no Booking history, the calculation fails as its dividing by zero and leaves a blank. I tried to include an IF statement to replace Null bookings with 100, otherwise continue with Abs(Booking-Forecast)/Bookings

I've included the expression below, but it still leaves a blank, instead of 100?

Content (please ensure you mask any confidential information):

If (Bookings History = null,100,(safe_division(abs(nvl(Bookings History,0) - nvl(Bookings Forecast,0)),Bookings History,0)*100))