Concat on empty rows

I’m trying to concat 3 columns together to get a unique identified.

column(“productcode”) + ‘*’ + column(“productsubcode”) + '*’ + column(“formcode”) + '*’ + column(“container_code”)

The issue is product sub code is not always populated so i get a value like this - productcode* formcodecontainercode. Is there way I can ignore blank rows when the product subcode isn’t populated and get a clean productcodeformcodecontainer?