else if

I have an external drive that is partitioned. One of the drives is PRO FULL 1 L. I want to be able to unmount the partition if it exists and do nothing if it does not exist. I have come up with the following which works fine if the partition exists, but can't figure out what to add to script (else if?) to deal with the situation if the partition does not exist. (running Catalina )

Thanks

---PRO FULL 1 L

if exists (do shell script "diskutil unmount /dev/disk4s2") then

end if

---PRO FULL 1 L - data

if exists (do shell script "diskutil unmount /dev/disk4s1") then

end if