HttpServer can not work when the ActorSystem name contains underscore

[FlyCoder]

I found that the HttpServer can not work when the ActorSystem name contains underscore.
And I debug it and find the ActorSystem name is treated as an URL host name and then parsed failed.
But the program does not give me any hint for this limit.

Test Code:
sbt-version: 2.11.11
colossus-version: 0.10.1

import scala.concurrent.duration._

import akka.actor.ActorSystem
import colossus.IOSystem
import colossus.core.{NoRetry, ServerContext, ServerRef, ServerSettings}
import colossus.parsing.DataSize
import colossus.protocols.http.HttpMethod.{Get, Post}
import colossus.protocols.http.{Http, HttpServer, Initializer, RequestHandler}
import colossus.service.GenRequestHandler.PartialHandler
import colossus.service.{Callback, ErrorConfig, ServiceConfig}

class TestServer(name: String)(implicit val actorSystem: ActorSystem) {

  class HttpRequestHandler(context: ServerContext, serviceConfig: ServiceConfig) extends RequestHandler(context, serviceConfig) {

    import colossus.protocols.http.UrlParsing._

    override def handle: PartialHandler[Http] = {
      case req@Get on Root => {
        Callback.successful(req.ok("ok"))
      }
      case req@Post on Root / "ack" => {
        println("received ack")
        Callback.successful(req.ok("ack"))
      }
    }
  }

  def start(port: Int): ServerRef = {
    implicit val ioSystem: IOSystem = IOSystem(name)
    val serviceConfig = ServiceConfig(
      2.minutes,
      4096,
      logErrors = true,
      requestMetrics = false,
      DataSize("1024 MB"),
      ErrorConfig(Set.empty, Set.empty)
    )

    HttpServer.start(name, ServerSettings.load(name).copy(port = port, bindingRetry = NoRetry)) { initContext =>
      new Initializer(initContext) {
        override def onConnect: ServerContext => RequestHandler =
          serverContext => new HttpRequestHandler(serverContext, serviceConfig)
      }
    }
  }

}

object TestServer {

  def main(args: Array[String]): Unit = {
    implicit val actorSystem: ActorSystem = ActorSystem("ab_cd")
    val ts = new TestServer("testServer")
    ts.start(9000)
  }

}

When I do post to http://localhost:9000/ack, I will get logs like below

[INFO] [09/04/2019 20:14:30.191] [ab_cd-akka.actor.default-dispatcher-11] [akka://ab_cd/deadLetters] Message [colossus.core.Worker$NewConnection] from Actor[akka://ab_cd/user/server-testServer#1510445994] to Actor[akka://ab_cd/deadLetters] was not delivered. [1] dead letters encountered. If this is not an expected behavior, then [Actor[akka://ab_cd/deadLetters]] may have terminated unexpectedly, This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
[INFO] [09/04/2019 20:14:30.192] [ab_cd-akka.actor.default-dispatcher-3] [akka://ab_cd/deadLetters] Message [colossus.core.Worker$NewConnection] from Actor[akka://ab_cd/user/server-testServer#1510445994] to Actor[akka://ab_cd/deadLetters] was not delivered. [2] dead letters encountered. If this is not an expected behavior, then [Actor[akka://ab_cd/deadLetters]] may have terminated unexpectedly, This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.