Moshi custom type adapter on Kotlin

ApiModels.kt

class RedditLink(
        val author: String,
        val likes: RedditLikes,
        val title: String,
        val score: Int
)

enum class RedditLikes {
    UP, DOWN, NONE
}

class LikesAdapter {
    @FromJson fun fromJson(likes: String): RedditLikes {
        Log.d("LikesAdapter", "I was called!!")
        when (likes) {
            "true"  ->  return RedditLikes.UP
            "false" ->  return RedditLikes.DOWN
            "null"  ->  return RedditLikes.NONE
            else -> {
                throw JsonDataException("likes could not be parsed: " + likes)
            }
        }
    }

    @ToJson fun toJson(likes: RedditLikes) = when(likes) {
        RedditLikes.UP -> "true"
        RedditLikes.DOWN -> "false"
        RedditLikes.NONE -> "null"
    }
}

MainActivity.kt

        val moshi = Moshi.Builder()
                .add(LikesAdapter())
                .build()

        val retrofit = Retrofit.Builder()
                .baseUrl("https://www.reddit.com")
                .addConverterFactory(MoshiConverterFactory.create(moshi))
                .build()