Empty less file causes Unexpected exception

[Enalmada]

It was nearly impossible for me to know why and what to do from this error after making lots of changes at the same time to migrate to new version of play. Who would have thought this error has anything to do with empty less file.

play.PlayExceptions$UnexpectedException: Unexpected exception[DeserializationException: Expected Int as JsNumber, but got null]
    at play.PlayReloader$$anon$1$$anonfun$play$PlayReloader$$anon$$taskFailureHandler$1.apply(PlayReloader.scala:236) ~[na:na]
    at play.PlayReloader$$anon$1$$anonfun$play$PlayReloader$$anon$$taskFailureHandler$1.apply(PlayReloader.scala:229) ~[na:na]
    at scala.Option.map(Option.scala:145) ~[scala-library-2.11.1.jar:na]
    at play.PlayReloader$$anon$1.play$PlayReloader$$anon$$taskFailureHandler(PlayReloader.scala:229) ~[na:na]
    at play.PlayReloader$$anon$1$$anonfun$reload$2.apply(PlayReloader.scala:89) ~[na:na]
Caused by: spray.json.DeserializationException: Expected Int as JsNumber, but got null
    at spray.json.package$.deserializationError(package.scala:23) ~[na:na]
    at spray.json.BasicFormats$IntJsonFormat$.read(BasicFormats.scala:29) ~[na:na]
    at spray.json.BasicFormats$IntJsonFormat$.read(BasicFormats.scala:25) ~[na:na]
    at spray.json.JsValue.convertTo(JsValue.scala:32) ~[na:na]
    at com.typesafe.sbt.jse.SbtJsTask$JsTaskProtocol$LineBasedProblemFormat$$anonfun$read$7.apply(SbtJsTask.scala:117) ~[na:na]

[huntc]

I'm not sure what to do about this other than suggest configuring the engine to use Node; perhaps the error output is better then. I'd be interested to know in case you'd care to try.

Right now we're translating errors reported from Trireme as per the following:

      script.execute.setListener(new ScriptStatusListener {
        def onComplete(script: NodeScript, status: ScriptStatus): Unit = {
          if (status.hasCause) {
            try {
              status.getCause match {
                case e: RhinoException =>
                  stderrOs.write(e.getLocalizedMessage.getBytes("UTF-8"))
                  stderrOs.write(e.getScriptStackTrace.getBytes("UTF-8"))
                case t =>
                  t.printStackTrace(new PrintStream(stderrOs))
              }
            } catch {
              case e: Throwable =>
                if (e.isInstanceOf[AskTimeoutException] || status.getCause.isInstanceOf[AskTimeoutException]) {
                  log.error(e, "Received a timeout probably because stdio sinks and sources were closed early given a timeout waiting for the JS to execute. Increase the timeout.")
                } else {
                  log.error(status.getCause, "Problem completing Trireme. Throwing exception, meanwhile here's the Trireme problem")
                  throw e
                }
            }
          }
          stdoutOs.close()
          stderrOs.close()
          senderSys.actorSelection(senderSel) ! status.getExitCode
        }
      })

@gbrail Do you have any other thoughts?

Closing for now though as I don't think this is something we can do anything about. Happy to re-open if it turns out that there is something to be done. Btw: JS itself is rubbish as a language in preventing this type of thing from happening. :-)