Serializer for Nothing not found

Describe the bug Using Nothing in a generic type argument fails with an internal error Serializer for element of type Nothing has not been found.

To Reproduce This reproduces the problem when compiling:

import kotlinx.serialization.Serializable

@Serializable
sealed class SerializableEither<out L, out R> {

    @Serializable
    data class Left<L>(val value: L) : SerializableEither<L, Nothing>()

    @Serializable
    data class Right<R>(val value: R) : SerializableEither<Nothing, R>()
}

Full compiler error: https://pastebin.com/FP6zGrDf

Expected behavior Nothing should be serializable.

Environment

• Kotlin version: 1.3.60
• Library version: 0.14.0
• Kotlin platforms: JVM
• Gradle version: 5.6.4
• IDE version (if bug is related to the IDE): IntelliJ IDEA 2019.2.4 (Ultimate Edition)
• Runtime version: 11.0.4+10-b304.77 amd64
• Linux 5.0.0-36-generic

[fluidsonic]

I’ve just started using kotlinx-serialization in a new project and this is basically the first issue I came across, with a compiler error that’s not very helpful (location: “File is unknown”).

Having a default serializer for Nothing would avoid that, wouldn’t it?

[sandwwraith]

So it would be basically like this:

object NotSerializable : KSerializer<Any> {
    override val descriptor: SerialDescriptor = SerialClassDescImpl( "kotlin.Any") 
    override fun deserialize(decoder: Decoder): Any = throw SerializationException("Not serializable")
    override fun serialize(encoder: Encoder, obj: Any) = throw SerializationException("Not serializable")
}

Such serializer can be applied for types in generic arguments (data class Left<L>(val value: L) : SerializableEither<L, @Serializable(NotSerializable::class) Nothing>()).

It even can be a default serializer for Nothing.