Problem with type converters

Gist.kt

//Database.kt
@Database(entities = [User::class], version = 1)
@TypeConverters(*[DatabaseTypeConverters::class])
abstract class Database : RoomDatabase() {
    abstract val userDao: UserDao
}

object DatabaseTypeConverters {
    @TypeConverter
    @JvmStatic
    fun userTypeListToString(types: List<UserType?>?): String =
            GsonBuilder().apply { registerAdapterFor<UserType>() }.create().toJson(types)

    @TypeConverter
    @JvmStatic
    fun stringToUserTypeList(name: String?): List<UserType?>? = name?.let {
        GsonBuilder().apply { registerAdapterFor<UserType>() }.create().fromJson(it)
    }
}

//UserData.kt
@Entity(tableName = UserDao.TABLE_NAME)
data class User @JvmOverloads constructor(
        @PrimaryKey @ColumnInfo(name = COLUMN_ID) var id: Long? = null,
        @ColumnInfo(name = COLUMN_NAME) var name: String? = null,
        @ColumnInfo(name = COLUMN_EMAIL) var email: String? = null,
        @ColumnInfo(name = COLUMN_TYPES) var types: List<UserType?>? = null
)

enum class UserType { GROWER, LAB, DISPENSARY, PATIENT, DOCTOR, SUPPLIER, TRANSPORTATION, GOVERNMENT }

object UserColumns {
    const val COLUMN_ID = "id"
    const val COLUMN_NAME = "name"
    const val COLUMN_EMAIL = "email"
    const val COLUMN_TYPES = "types"
}

//GsonExt.kt
internal inline fun <reified T : Enum<T>> GsonBuilder.registerAdapterFor() {
    registerTypeAdapter(T::class.java, JsonDeserializer { json, _, _ -> parseEnum<T>(json) })
}

private inline fun <reified T : Enum<T>> parseEnum(json: JsonElement): Enum<T>? = try {
    enumValueOf<T>(json.asString.toUpperCase())
} catch (e: Exception) {
    null
}

inline fun <reified T> Gson.fromJson(json: String): T =
        this.fromJson<T>(json, object : TypeToken<T>() {}.type)

/*
 * Getting this error:
 * Cannot figure out how to save this field into database. You can consider adding a type converter for it.
 * 
 * Error corresponds to 'types' property of User
 */