Play OAuth NPE

NPE.scala

package controllers

import play.api._
import play.api.mvc._
import play.api.libs.oauth._
import play.api.libs.ws.WS

object Application extends Controller {

  object MyApi {
    private val ReqSigner = OAuthCalculator(
      ConsumerKey("fake", "secret"), RequestToken("", ""))

    def call(params: Map[String, Seq[String]] = Map.empty) = {
      WS.url("http://api.example.com/v2")
        .sign(ReqSigner)
        .post(params)
    }
  }

  def index = Action { Async {
    MyApi.call(Map("foo" -> Seq("bar"))).map(_ => Ok("done"))
  }}
}