Ktor serialization question

I have a data class that models a response from Firebase on user sign in. It looks like the following:

@Serializable data class SignInResponse( val kind: String? = null, val localId: String? = null, val email: String? = null, val displayName: String? = null, val idToken: String? = null, val registered: Boolean? = null, val error: ErrorResponse? = null } 

On my httpClient I have set it up like so:

val httpClient = HttpClient(CIO) { install(ContentNegotiation) { json(Json { ignoreUnknownKeys = true }) } // other config here... } 

I am using kotlinx.serialization

I have another class FirebaseAuthenticationClient that uses that httpClient to make requests into Firebase.

My question is, is there a way to not have to mark all properties in the SignInResponse class nullable and give a default value of null? I would prefer it if the serializer handled this automatically and if a property on the response wasn’t present, it nulled it by default without me having to explicity mark it as so. As it stands, an exception is thrown every time I remove ?. I thought that was the purpose of ignoreUnknownKeys, but that does not seem to be the case.

Coming from C# this seems very weird to me as this would be handled automatically and here I’m trying to avoid having to mark all properties as nullable across all my response objects.