Scalatra servlet with failing JSON serialization

BibRouter.scala

package router

import service.BibService
import model.Bib
import org.scalatra.swagger.Swagger
import spray.json._
import DefaultJsonProtocol._
import format.ApiFormats._

/**
 * @version $Id$ $Rev: 223159 $ $Date: 2013-11-27 15:12:03 -0800 (Wed, 27 Nov 2013) $
 */
class BibRouter(config: {
  val swagger: Swagger
  val bibService: BibService
})
  extends RouterBase(config.swagger) {

  protected def applicationDescription: String = "Bibliographic data API"

  get("/", operation(apiOperation[List[Bib]]("getBibs")
    summary "Get all bibs")) {
    config.bibService.allBibs.toJson
  }

  get("/:id", operation(apiOperation[Bib]("getBib")
    summary "Get a bib")) {
    config.bibService.getBib(Integer.parseInt(params("id"))).toJson
  }

  get("/ids", operation(apiOperation[List[Int]]("allBibIds")
    summary "Get all bib IDs")) {
    config.bibService.allBibIds.toJson
  }
}