I need a formula that, when I subtract two numbers, the answer is not a negative number, but shows up as "empty"

so, in this way, when the property is empty I'll not show up in the place

like "if the death part is empty, substract "year", "born", but if the death shows up, substract "death", "born""

(i try to write this on formula but i can get it right, so please, helpp)