Why Kotlin does not have

Either

class? https://www.scala-lang.org/api/2.9.3/scala/Either.html

It's not trying to be fully functional. Doesn't have option, try and others either. If you want that, the 'standard' is arrow-kt. #arrow

Well, it has Option as nullable types

I believe Kotlin way might be to use sealed classes. One benefit is you can even add 3rd case hopefully without too much code change.

Just for completeness' sake, nullable types in Kotlin are not really equivalent to a dedicated

Option

class, most notably because they can't be nested without losing information