Error when using TypeConverter with Room: Cannot figure out how to save this field into database

I get this error:

error: Cannot figure out how to save this field into database. You can consider adding a type converter for it. private final java.util.List<com.example.Detail.Stat> stats = null;

I can't figure it out. I have Added the typeconverter to the database, but still get this error. Any ideas what I do wrong?

Entity:

@Entity
data class Detail(
    @PrimaryKey val id: Int,
    val stats: List<Stat>,
    val types: List<String>

){
    data class Stat(
        val baseStat: Int,
        val stat: String
    )
}

Typeconverter:

@ProvidedTypeConverter
class StatConverter @Inject constructor(
    private val moshi: Moshi
){
    @TypeConverter
    fun fromJson(value: String): List<Detail.Stat>? {
        val listType = Types.newParameterizedType(List::class.java, Detail.Stat::class.java)
        val adapter: JsonAdapter<List<Detail.Stat>> = moshi.adapter(listType)
        return adapter.fromJson(value)
    }
    @TypeConverter
    fun toJson(type: List<Detail.Stat>?): String {
        val listType = Types.newParameterizedType(List::class.java, Detail.Stat::class.java)
        val adapter: JsonAdapter<List<Detail.Stat>> = moshi.adapter(listType)
        return adapter.toJson(type)
    }
}

Database:

@Database(entities = [Detail::class], version = 1, exportSchema = true)
@TypeConverters(StatConverter::class)
abstract class Database : RoomDatabase() {

    abstract fun detailDao(): DetailDao

    companion object{
        const val DATABASE = "database"
    }

}

DI module where room is provided:

@Singleton
    @Provides
    fun provideAppDatabase(
        application: Application,
        statConverter: StatConverter
    ): Database {
        return Room
            .databaseBuilder(application, Database::class.java,
                Database.DATABASE
            )
            .addTypeConverter(statConverter)
            .fallbackToDestructiveMigration()
            .build()
    }

EDIT:

The typeconverter code works fine with the other field (List) in the entity, but not with List.

Apparently, something about your nested data class is causing problems, and so moving Stat out from being nested in Detail helped.

If you have the time, you might try creating a scrap project that illustrates the problem, then file an issue on the issue tracker, attaching that project as a demonstration of the problem. I don't see anything that quite matches, but there are a lot of issues, so perhaps I missed it.