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kotlinlang

I'm hitting an odd issue where a class can't seem to serialize itself, or at least it's not serializing its backing fields. It's a small class:
```@Serializable
class GameState {
    var playerName = "Dougie McDougal"
    @Transient
    var saveFileName = "save1"

    suspend fun save() {
        println("Saving game state $saveFileName.gs.json")
        val gameStateJson = Json.encodeToString(this@GameState)
        val saveFile = applicationVfs["saves/$saveFileName.gs.json"]
        saveFile.write(gameStateJson.toByteArray())
    }
}```
The serialized output is just `{}` - empty. `playerName` is not being serialised. Any thoughts?

According to <https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/basic-serialization.md#json-decoding> backing fields like `playerName` should be serialized.

Adding the `@Required` annotation has solved this, though the documentation doesn't make that explicitly needed.

I believe default values are omitted by default - its configurable by a flag OR by explicitly marking field required so it will always be present