HTTP 헤더 이름은 왜 타입을 안만드나?

Headers.kt

class Http {
    data class HeaderName(val name: String) : Comparable<HeaderName> {
        override fun compareTo(other: HeaderName): Int = name.compareTo(other.name, true)

        fun get(headers: MultiMap): String? = headers.get(name)
        fun set(headers: MultiMap, value: String): Unit { headers.set(name, value) }

        fun copyIfExist(from: MultiMap, to: MultiMap) {
            get(from)?.let { set(to, it) }
        }
    }

    class Headers {
        companion object {
            @JvmField
            val CONTENT_TYPE = HeaderName("Content-Type")

            @JvmField
            val HOST = HeaderName("Host")
        }
    }
}

ProxyPassHandler.kt

class ProxyPassHandler(private val config: Config, private val webClient: WebClient) : Handler<RoutingContext> {
    data class Config(var upstreamUrl: String) {
        constructor() : this("http://upstream")
    }

    private val logger = LoggerFactory.getLogger(javaClass)

    override fun handle(context: RoutingContext) {
        val request = context.request()
        val response = context.response()
        val uri = config.upstreamUrl
        logger.debug("Upstream URI {}", uri)
        request.bodyHandler()
            .flatMap { body ->
                webClient.postAbs(uri)
                    .apply {
                        Http.Headers.CONTENT_TYPE.copyIfExist(request.headers(), headers())
                    }
                    .sendBuffer(body)
            }
            .map {
              logger.debug("Upstream response {}: {}", it.statusCode(), it.bodyAsString())
              it.bodyAsJsonObject()
            }
            .map { ApiResponse.Success(it) }
            .subscribe({
                response
                    .putHeader(Http.Headers.CONTENT_TYPE.name, Http.MimeType.JSON)
                    .end(Json.encodeToBuffer(it))
            }, {
                context.fail(it)
            })
    }
}