How to set empty string as a custom value?

Hi everyone!

I’m trying to filter a psql query by languange

I have a custom variable with this values:
All : “”, Italian : ‘it’, French : ‘fr’

This is the part of the query where I use it:
name = ‘${Language:value}Book’

Expecting the query would be, in the same order:
name = ‘Book’
name = ‘itBook’
name = ‘frBook’

However, the first is name = ‘""Book’

Is there a way to have an empty string as the value of All? I’ve also tried to use a custom value for All, but with no success.