Alexander Yevsyukov

As a suggestion, what if the initial stable release would do what Immutable Collections from Guava do, so that existing Java code can be migrated to Kotlin easier?

There is a `GreedyPolicy` test env. class in ProtoData code with the associated test. It should be migrated to `core-java` as an additional result of this issue.

To be mentioned as breaking change in [Release Notes](https://github.com/SpineEventEngine/SpineEventEngine.github.io/issues/409).

> Triplet This does not make much sense. It's a `Pair`. But your request does make sense. How often do you need such a thing? Depending on the answer, we'd...

Suggested alternative name: `None`.

Previously suggested empty `Tuple` type won't work because our `Nothing` is frequently used in tules like this: `EitherOf2`.

We currently have two `typealias`-es called `NothingHappened` and `NoReaction`. This should ease the name clash with the standard Kotlin type. See the `io.spine.server.model.EventExts.kt` file for details.

> Therefore, I'd stick to `NoReaction` as a `typealias`. And I would drop `NothingHappened`. Yeah, see this [commit](https://github.com/SpineEventEngine/core-java/pull/1549/commits/039768068c649b065b4ffd0668c098ad7503d5a9).

Resolved by #1554.

It can be made via a mix-in interface. We know the name of the type, we can obtain the descriptor of the message. Get the field reference and see if...