I'm getting the error

Caused by: kotlinx.serialization.json.internal.JsonDecodingException: Polymorphic serializer was not found for missing class discriminator ('null')

I know that the type field in my json data is missing, however I set up a default deserializer for it.

polymorphicDefaultDeserializer(ApiNext.Renderer.ItemSection::class) {
  ApiNext.Renderer.Separator.serializer()
}

This should work, but it throws that error. ItemSection is a sealed interface Seperator is just a serializable object that inherits from it