You are close here! the “is_known” operator is what you’ll need to incorporate here. However, it returns a boolean, meaning that you’ll need to add this throughout your formula to return results as desired. When using this check for null values, use && instead of == to determine if there is a value there FIRST, then move onto your decisions of what to do if a value is there. The function to check if a value is there or not should look like the below:
if(is_known([property])&&true,[value if true], [value if false])
you can use the above in the middle of your formula and add nested if statements to get your formula working as needed