Scsi address and null field issues when adding drives

I have got a spreasheet and it requires up to 6 drives to be added to a list of VMs.

vmname, hdd1, hdd2, hdd3, hdd4, hdd5, hdd6. I then want to run another command if hdd2 exists lets say its to return "disk two exists"

hdd1 always needs to be mapped to scsi 0:3,

hdd2 always needs to be mapped to scsi 0:4 etc.

but sometime there is a hdd1 and a hdd3 and hdd6 but no hdd2 or hdd 4.

I have two problems

I don't know how to ensure the drive gets assigned the write scsi address.

I don't know how to do or not do things if fields are null or not.

Please help.