Moshi json adapter factory for KotlinX's ImmutableList

ImmutableListJsonAdapterFactory.kt

import com.squareup.moshi.JsonAdapter
import com.squareup.moshi.JsonReader
import com.squareup.moshi.JsonWriter
import com.squareup.moshi.Moshi
import com.squareup.moshi.rawType
import kotlinx.collections.immutable.ImmutableList
import kotlinx.collections.immutable.persistentListOf
import java.lang.reflect.ParameterizedType
import java.lang.reflect.Type

object ImmutableListJsonAdapterFactory : JsonAdapter.Factory {

    override fun create(type: Type, annotations: MutableSet<out Annotation>, moshi: Moshi): JsonAdapter<*>? {
        if (!ImmutableList::class.java.isAssignableFrom(type.rawType) ||
            type !is ParameterizedType
        ) {
            return null
        }
        val elementType = type.actualTypeArguments[0]
        val elementAdapter = moshi.adapter(elementType.rawType)
        return Adapter(elementAdapter)
    }

    private class Adapter<E>(private val elementAdapter: JsonAdapter<E>) : NullSafeJsonAdapter<ImmutableList<E>>() {

        override fun readFrom(reader: JsonReader): ImmutableList<E> {
            val listBuilder = persistentListOf<E>().builder()
            reader.beginArray()
            while (reader.hasNext()) {
                listBuilder.add(elementAdapter.fromJson(reader)!!)
            }
            reader.endArray()
            return listBuilder.build()
        }

        override fun writeTo(writer: JsonWriter, value: ImmutableList<E>) {
            writer.beginArray()
            for (element: E in value) {
                elementAdapter.toJson(writer, element)
            }
            writer.endArray()
        }
    }
}