Revert nullable return in getFinalizedVersion

What impact does this have on 🐛 Update method `getAsset` signature with appropriate changes Active ? Is it a temporary solution until that issue is fixed?

getAsset has had that method signature since the beginning of Acquia DAM, with the problem being this internal method returning an invalid version ID. Any methods calling getAsset should ensure that $version_id is either omitted or is a string.

Will mark the other issue "Closed, works as designed".

Automatically closed - issue fixed for 2 weeks with no activity.