title: What is a Boxed Error in Scala?
body: <p>When I run my application, the browser shows </p>
  
  <pre><code>[ExecutionException: Boxed Error]
  </code></pre>
  
  <p>It doesn't say anything about the line number, etc.</p>
  
  <p>In the console, I have the following</p>
  
  <pre><code>! @6elaah0c8 - Internal server error, for (GET) [/testlearn] -&gt;
  
  play.api.Application$$anon$1: Execution exception[[ExecutionException: Boxed Error]]
      at play.api.Application$class.handleError(Application.scala:289) ~[play_2.10.jar:2.1.1]
      at play.api.DefaultApplication.handleError(Application.scala:383) [play_2.10.jar:2.1.1]
      at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$17$$anonfun$apply$24.apply(PlayDefaultUpstreamHandler.scala:326) [play_2.10.jar:2.1.1]
      at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$17$$anonfun$apply$24.apply(PlayDefaultUpstreamHandler.scala:324) [play_2.10.jar:2.1.1]
      at play.api.libs.concurrent.PlayPromise$$anonfun$extend1$1.apply(Promise.scala:113) [play_2.10.jar:2.1.1]
      at play.api.libs.concurrent.PlayPromise$$anonfun$extend1$1.apply(Promise.scala:113) [play_2.10.jar:2.1.1]
  java.util.concurrent.ExecutionException: Boxed Error
      at scala.concurrent.impl.Promise$.resolver(Promise.scala:52) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at scala.concurrent.impl.Promise$.scala$concurrent$impl$Promise$$resolveTry(Promise.scala:44) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:116) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at scala.concurrent.Promise$class.complete(Promise.scala:55) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:58) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:23) [factorie-1.0.0-M4-jar-with-dependencies.jar:na]
  Caused by: java.lang.AssertionError: assertion failed
      at scala.Predef$.assert(Predef.scala:165) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at cc.factorie.util.TraversableExtras$class.max2ByDouble(TraversableExtras.scala:95) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at cc.factorie.package$$anon$2.max2ByDouble(package.scala:148) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at cc.factorie.optimize.SampleRankExample.accumulateExampleInto(SampleRank.scala:31) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at cc.factorie.optimize.OnlineTrainer$$anonfun$processExamples$3.apply(Trainer.scala:72) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
      at cc.factorie.optimize.OnlineTrainer$$anonfun$processExamples$3.apply(Trainer.scala:63) ~[factorie-1.0.0-M4-jar-with-dependencies.jar:na]
  </code></pre>