title: GWT Uncaught IllegalArgumentException
body: <p>Sometimes my GWT app reports an "Uncaught IllegalArgumentException" below. The error log effectively masks any possible cause from the app. How would you pin down the source of the problem pragmatically in this case?</p>
  
  <pre><code>[ERROR] [mygwtapp] Uncaught exception escaped
  
  java.lang.IllegalArgumentException: Something other than a Java object was returned from JSNI method '@com.google.gwt.core.client.impl.Impl::apply(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)': JS value of type boolean, expected java.lang.Object
      at com.google.gwt.dev.shell.JsValueGlue.get(JsValueGlue.java:178)
      at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:271)
      at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
      at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
      at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
      at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
      at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
      at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
      at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:292)
      at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546)
      at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
      at java.lang.Thread.run(Thread.java:662)
  </code></pre>