```var writeType: (KType) -> String = { ...

# multiplatform

[josephivie]

var writeType: (KType) -> String = {
        ((it.classifier as? KClass<*>)
                ?.let { ExternalTypeRegistry[it] } ?: "Unit") +
                if (it.isMarkedNullable) "?" else ""
    }

JsonSerializer.kt: (11, 14): Unsupported [This reflection API is not supported yet in JavaScript]

(referring to it.classifier)