Skip the null variable

Hi

I have a script to create a new hard disk for the VM

How to modify my script to skip the the harddisk creation if the hardisk1 cell does not have a value(empty)!

$harddisk1 = $Data.harddisk1
$DatastoreName1 = $Data.DatastoreName1

$Name | New-HardDisk -CapacityGB $harddisk1 -Datastore $DatastoreName1 -Persistence persistent