await on a Future[Nothing] can cause NotImplementedError

[ewiner]

I have some code that makes an async call do decide which exception to throw. This seems to generate an assignment to ??? in the calling method when that exception state is skipped.

import scala.async.Async._
import scala.concurrent.duration.Duration
import scala.concurrent.{Await, Future}
import scala.concurrent.ExecutionContext.Implicits.global

def errorGenerator(randomNum: Double) = {
  Future {
    if (randomNum < 0) {
      throw new IllegalStateException("Random number was too low!")
    } else {
      throw new IllegalStateException("Random number was too high!")
    }
  }
}
def randomTimesTwo = async {
  val num = math.random
  if (num < 0 || num > 1) {
    await(errorGenerator(num))
  }

  num * 2
}

println(Await.result(randomTimesTwo, Duration("1 second")))

results in

java.util.concurrent.ExecutionException: Boxed Error
    at scala.concurrent.impl.Promise$.resolver(Promise.scala:55)
    at scala.concurrent.impl.Promise$.scala$concurrent$impl$Promise$$resolveTry(Promise.scala:47)
    at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:244)
    at scala.concurrent.Promise$class.complete(Promise.scala:55)
    at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:153)
    at A$A110$A$A110$stateMachine$macro$1$1.resume(playground.sc0.tmp:20)
    at A$A110$A$A110$stateMachine$macro$1$1.resume(playground.sc0.tmp:20)
    at A$A110$A$A110$stateMachine$macro$1$1.apply$mcV$sp(playground.sc0.tmp:20)
    at A$A110$A$A110$stateMachine$macro$1$1.apply(playground.sc0.tmp:20)
    at A$A110$A$A110$stateMachine$macro$1$1.apply(playground.sc0.tmp:20)
    at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
    at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
    at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:121)
    at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
    at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
    at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
    at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
Caused by: scala.NotImplementedError: an implementation is missing
    at scala.Predef$.$qmark$qmark$qmark(Predef.scala:225)
    ... 12 more

Tried this on async 0.9.2 & 0.9.3, Scala 2.11.4.

[retronym]

Darn, I thought I'd fixed this as #66.