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kotlinlang

Hi all. I'm getting
```kotlinx.serialization.json.internal.JsonEncodingException: Value of type 'kotlinx.serialization.Polymorphic&lt;IdType&gt;' can't be used in JSON as a key in the map. It should have either primitive or enum kind, but its kind is 'OPEN'.```
where
```interface IdType : Parcelable {
  val name: String
}

enum class PersonIdType : IdType {
  GIVEN_NAME, MIDDLE_NAMES, FAMILY_NAME
}

enum class VehicleIdType : IdType {
  PLATE_NUMBER, VIN, ENGINE_NUMBER,
}```
is this a known limitation? :thinking_face:

You're asking for too much there. When you serialise an `IdType` the result is going to be an object and not a string. JSON doesn't allow object keys.

You'll need to write a custom serialiser for `IdType` to achieve what you want.

yeah makes sense. With a custom serialiser that serialise the idType to a string, it works as expected :thumbsup: