[Q] How to batch change genre to = sub-genre then wipe sub-genre

Hi all, I'm trying to find the best way to batch change my songs' existing sub-genres [ContentGroup]
and make those/promote them to genres [GENRE] and then clear out the sub-genre field.

The only gotcha is I don't want a blank sub-genre to erase an existing genre. Is this possible w/ actions? Thanks!

For example:

Artist Song Genre Sub-Genre/ContentGroup
Depeche Mode Wrong Electronica Synthpop
Depeche Mode Wrong Synthpop

Yazoo Situation Electronica
Yazoo Situation Electronica

make an action group:

Action: Format Value
Field: GENRE
Format String: $if2(%contentgroup%,%genre%)

Action: Remove Fields
Fileds to remove: CONTENTGROUP