Not that this reveals much, but the full stack trace is below.
at sbt.PlayReloader$$anon$2.reload(PlayReloader.scala:296) ~[na:na]
at play.core.ReloadableApplication$$anonfun$get$1.apply(ApplicationProvider.scala:95) ~[play_2.9.2.jar:2.1-SNAPSHOT]
at play.core.ReloadableApplication$$anonfun$get$1.apply(ApplicationProvider.scala:93) ~[play_2.9.2.jar:2.1-SNAPSHOT]
at akka.dispatch.Future$$anon$3.liftedTree1$1(Future.scala:195) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.dispatch.Future$$anon$3.run(Future.scala:194) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:94) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.jsr166y.ForkJoinTask$AdaptedRunnableAction.exec(ForkJoinTask.java:1381) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.jsr166y.ForkJoinTask.doExec(ForkJoinTask.java:259) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.jsr166y.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:975) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.jsr166y.ForkJoinPool.runWorker(ForkJoinPool.java:1479) ~[akka-actor-2.0.2.jar:2.0.2]
at akka.jsr166y.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:104) ~[akka-actor-2.0.2.jar:2.0.2]
at scala.Function2$$anonfun$tupled$1.apply(Function2.scala:51) ~[scala-library.jar:0.12.0]
at scala.Function2$$anonfun$tupled$1.apply(Function2.scala:50) ~[scala-library.jar:0.12.0]
at scala.collection.immutable.Stream.foreach(Stream.scala:526) ~[scala-library.jar:0.12.0]
at sbt.Sync$$anonfun$apply$1.apply(Sync.scala:44) ~[na:na]
at sbt.Sync$$anonfun$apply$1.apply(Sync.scala:23) ~[na:na]
at sbt.PlayCommands$$anonfun$9.apply(PlayCommands.scala:150) ~[na:na]
at sbt.PlayCommands$$anonfun$9.apply(PlayCommands.scala:131) ~[na:na]
at sbt.Scoped$$anonfun$hf9$1.apply(Structure.scala:585) ~[na:na]
at sbt.Scoped$$anonfun$hf9$1.apply(Structure.scala:585) ~[na:na]
at scala.Function1$$anonfun$compose$1.apply(Function1.scala:49) ~[scala-library.jar:0.12.0]
at sbt.Scoped$Reduced$$anonfun$combine$1$$anonfun$apply$12.apply(Structure.scala:311) ~[na:na]
at sbt.Scoped$Reduced$$anonfun$combine$1$$anonfun$apply$12.apply(Structure.scala:311) ~[na:na]
at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:41) ~[na:na]
at sbt.std.Transform$$anon$
5.work(System.scala:71) ~[na:na]
at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:232) ~[na:na]
at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:232) ~[na:na]
at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18) ~[na:na]
at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:232) ~[na:na]
at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:232) ~[na:na]
at sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:159) ~[na:na]
at sbt.CompletionService$$anon$2.call(CompletionService.scala:30) ~[na:na]
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) ~[na:1.7.0_04]
at java.util.concurrent.FutureTask.run(FutureTask.java:166) ~[na:1.7.0_04]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) ~[na:1.7.0_04]
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) ~[na:1.7.0_04]
at java.util.concurrent.FutureTask.run(FutureTask.java:166) ~[na:1.7.0_04]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) [na:1.7.0_04]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) [na:1.7.0_04]
at java.lang.Thread.run(Thread.java:722) [na:1.7.0_04]