Klaxon parse null enum - kotlin

Question

I am trying to parse a json response that include an enum using the Klaxon library and kotlin. Below is a test. If I have a nullable enum, my parsing fails. Is there a way to do this properly? Is it an issue with the Klaxon libary?
import com.beust.klaxon.Klaxon
import org.junit.jupiter.api.Test
import kotlin.test.assertEquals
import kotlin.test.assertNotNull
import kotlin.test.assertNull
enum class MyEnum { FIRST, SECOND, THIRD }
class WithEnum {
var myVal: MyEnum? = null
}
class EnumTest {
#Test
fun `should deserialize null enum`() {
val parsed = Klaxon().parse<WithEnum>("{ \"myVal\":null}")
assertNotNull(parsed)
assertNull(parsed.myVal)
}
#Test
fun `should deserialize proper enum`() {
val parsed = Klaxon().parse<WithEnum>("{ \"myVal\":\"FIRST\"}")
assertNotNull(parsed)
assertEquals(MyEnum.FIRST, parsed.myVal)
}
}
The response from the above unit test is:
kotlin.TypeCastException: null cannot be cast to non-null type kotlin.String
at com.beust.klaxon.EnumConverter.fromJson(EnumConverter.kt:23)
at com.beust.klaxon.EnumConverter.fromJson(EnumConverter.kt:6)
at com.beust.klaxon.JsonObjectConverter.retrieveKeyValues(JsonObjectConverter.kt:189)
at com.beust.klaxon.JsonObjectConverter.initIntoUserClass(JsonObjectConverter.kt:67)
at com.beust.klaxon.JsonObjectConverter.fromJson(JsonObjectConverter.kt:32)
at com.beust.klaxon.DefaultConverter.fromJsonObject(DefaultConverter.kt:210)
at com.beust.klaxon.DefaultConverter.fromJson(DefaultConverter.kt:32)
at com.beust.klaxon.Klaxon.fromJsonObject(Klaxon.kt:296)
at EnumTest.should deserialize null enum(EnumTest.kt:30)
...
There source of the error is https://github.com/cbeust/klaxon/blob/master/klaxon/src/main/kotlin/com/beust/klaxon/EnumConverter.kt#L23, where the null is being cast to a String.

Answer 1

I copied the EnumConverter from the github project and made it nullable, changing line 23 to return a null if the value is a null like so:
val name = jv.inside as String? ?: return null
I then created an annotation for the fields and added the converter to the parser. The EnumConverter() reference below is my copy of it with the Elvis operator addition above.
...
#Target(AnnotationTarget.FIELD)
annotation class NullableEnum
class WithEnum (
#NullableEnum
var myVal: MyEnum? = null
)
class EnumTest {
#Test
fun `should deserialize null enum`() {
val parsed = Klaxon()
.fieldConverter(NullableEnum::class, EnumConverter())
.parse<WithEnum>("{ \"myVal\":null}")
assertNotNull(parsed)
assertNull(parsed.myVal)
}
...