println "hello" ... in web-console causes unhandled exception on the server side

[paul-hammant]

Groovy 2.4.5, JDK 9-ea, Gradle 2.11

[ratpack-compute-1-1] ERROR ratpack.error.internal.DefaultDevelopmentErrorHandler - exception thrown for request to /execute
ratpack.render.RendererException: Renderer 'ratpack.example.groovywebconsole.ScriptResultRenderer@3b9f982' failed to render 'ratpack.example.groovywebconsole.ScriptResult@5ed2929f'
    at ratpack.render.internal.DefaultRenderController.doRender(DefaultRenderController.java:71)
    at ratpack.render.internal.DefaultRenderController.doRender(DefaultRenderController.java:58)
    at ratpack.render.internal.DefaultRenderController.render(DefaultRenderController.java:43)
    at ratpack.handling.internal.DefaultContext.render(DefaultContext.java:270)
    at ratpack.groovy.handling.internal.DefaultGroovyContext.render(DefaultGroovyContext.java:161)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:520)
    at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
    at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:324)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:382)
    at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1016)
    at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:66)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:163)
    at ratpack$_run_closure1$_closure3$_closure6$_closure9.doCall(ratpack.groovy:25)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:520)
    at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
    at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:324)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:292)
    at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1016)
    at groovy.lang.Closure.call(Closure.java:423)
    at org.codehaus.groovy.runtime.ConvertedClosure.invokeCustom(ConvertedCjava:51)
    at org.codehaus.groovy.runtime.ConversionHandler.invoke(ConversionHandler.java:103)
    at com.sun.proxy.$Proxy14.execute(Unknown Source)
    at ratpack.exec.internal.DefaultPromise$1.success(DefaultPromise.java:42)
    at ratpack.exec.Promise.lambda$null$33(Promise.java:239)
    at ratpack.exec.Downstream$1.success(Downstream.java:72)
    at ratpack.exec.internal.DefaultExecution$2.lambda$success$128(DefaultExecution.java:174)
    at ratpack.exec.internal.DefaultExecution$StreamHandle.lambda$complete$132(DefaultExecution.java:224)
    at ratpack.exec.internal.DefaultExecution.intercept(DefaultExecution.java:359)
    at ratpack.exec.internal.DefaultExecution.intercept(DefaultExecution.java:331)
    at ratpack.exec.internal.DefaultExecution.drain(DefaultExecution.java:300)
    at ratpack.exec.internal.DefaultExecution.<init>(DefaultExecution.java:103)
    at ratpack.exec.internal.DefaultExecController$1.start(DefaultExecController.java:178)
    at ratpack.handling.internal.DefaultContext.start(DefaultContext.java:159)
    at ratpack.server.internal.NettyHandlerAdapter.channelRead0(NettyHandlerAdapter.java:131)
    at ratpack.server.internal.NettyHandlerAdapter.channelRead0(NettyHandlerAdapter.java:53)
    at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
    at ratpack.server.internal.NettyHandlerAdapter.channelRead(NettyHandlerAdapter.java:85)
    at io.netty.channel.ChannelHandlerInvokerUtil.invokeChannelReadNow(ChannelHandlerInvokerUtil.java:83)
    at io.netty.channel.DefaultChannelHandlerInvoker$7.run(DefaultChannelHandlerInvoker.java:158)
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:322)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:356)
    at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:703)
    at ratpack.exec.internal.DefaultExecController$ExecControllerBindingThreadFactory.lambda$newThread$139(DefaultExecController.java:116)
    at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDr.run(DefaultThreadFactory.java:137)
    at java.lang.Thread.run(Thread.java:804)
Caused by: java.lang.ClassCastException: [B cannot be cast to [C
    at groovy.json.internal.FastStringUtils$StringImplementation$1.toCharArray(FastStringUtils.java:89)
    at groovy.json.internal.FastStringUtils.toCharArray(FastStringUtils.java:174)
    at groovy.json.internal.CharBuf.addJsonFieldName(CharBuf.java:515)
    at groovy.json.JsonOutput.writeMap(JsonOutput.java:420)
    at groovy.json.JsonOutput.writeObject(JsonOutput.java:291)
    at groovy.json.JsonOutput.toJson(JsonOutput.java:184)
    at ratpack.example.groovywebconsole.ScriptResultRenderer$_render_closure1$_closure2.doCall(ScriptResultRenderer.groovy:16)
    at ratpack.example.groovywebconsole.ScriptResultRenderer$_render_closure1$_closure2.doCall(ScriptResultRenderer.groovy)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:520)
    at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
    at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:324)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:292)
    at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1016)
    at groovy.lang.Closure.call(Closure.java:423)
    at org.codehaus.groovy.runtime.ConvertedClosure.invokeCustom(ConvertedClosure.java:51)
    at org.codehaus.groovy.runtime.ConversionHandler.invoke(ConversionHandler.java:103)
    at com.sun.proxy.$Proxy32.execute(Unknown Source)
    at ratpack.handling.internal.ContentNegotiationHandler.handle(ContentNegotiationHandler.java:61)
    at ratpack.handling.internal.DefaultContext.byContent(DefaultContext.java:421)
    at ratpack.groovy.handling.internal.DefaultGroovyContext.byContent(DefaultGroovyContext.java:79)
    at ratpack.example.groovywebconsole.ScriptResultRenderer.render(ScriptResultRenderer.groovy:14)
    at ratpack.example.groovywebconsole.ScriptResultRenderer.render(ScriptResultRenderer.groovy)
    at ratpack.groovy.render.GroovyRendererSupport.render(GroovyRendererSupport.java:39)
    at ratpack.render.internal.DefaultRenderController.doRender(DefaultRenderController.java:68)
    ... 50 more