typesafe config - prefer empty value over fallback

Question

having config A:

akka {
  cluster {} //empty
}

and config B:

akka {
  cluster { some = thing } //non empty
}

I would like to get akka.cluster = empty - taken from first object A when merging them, e.g.

val config = A.withFallback(B). // prefers A over B... but

but when merging happens, it recursively goes into the contents of A/B and it then compares null field from A with non-null field of B and thus returns contents of B.

Long story short: empty object does NOT take priority over non-empty object

Is there a way to make sure that empty A takes over the non-empty B?

thanks

ps: it's a simplified example. I need to merge a more complex A with a more complex B, so I am looking for a general solution