Stuck on If, then, else

Hello - very new to Calibre, but very familiar with data manipulation. I am trying to create a custom field using if-then-else. I have spent days searching and cannot figure out the correct syntax.

Here is what I am trying to solve for:

IF {universe} isempty

THEN concatenate({universe},{book#})

ELSE concatenate ("1",{author},{saga},{Book#}

Any help is greatly appreciated!!