https://github.com/bitcoin/bitcoin/pull/19806/commits/f6e2da5fb7c6406c37612c838c998078ea8d2252
> Don't return null snapshotblockhash values to avoid caller complexity/confusion.
https://github.com/bitcoin/bitcoin/pull/21681/commits/931684b24a89aba884cb18c13fa67ccca339ee8c
> validation: fix ActivateSnapshot to use hardcoded nChainTx
>
> This fixes an oversight from the move of nChainTx from the user-supplied
> snapshot metadata into the hardcoded assumeutxo chainparams.
>
> Since the nChainTx is now unused in the metadata, it should be removed
> in a future commit.
https://github.com/bitcoin/bitcoin/pull/21681/commits/91d93aac4e3fe6fff5ef492ed152c4d8fa6f2672
> validation: remove nchaintx from assumeutxo metadata
>
> This value is no longer used and is instead specified statically
> in chainparams. This change means that previously generated
> snapshots will no longer be usable.
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19806 | core#19806]] [5/8] and core#21681 (partial)
https://github.com/bitcoin/bitcoin/pull/19806/commits/f6e2da5fb7c6406c37612c838c998078ea8d2252
The test related changes from core#21681 are in D11421