JRuby+Processing error

#!/usr/bin/env jruby
require "java"

include_class "processing.core.PApplet"

class Sketch < PApplet

  def setup
    size( 300, 300, P3D )
    no_stroke
    color_mode RGB, 1

    @xmag = 0
    @ymag = 0
    @newXmag = 0
    @newYMag = 0
  end

  def draw
    background 0.5, 0.5, 0.45

    push_matrix 

    translate(width/2, height/2, -30)

    @newXmag = mouseX/width.to_f * TWO_PI;
    @newYmag = mouseY/height.to_f * TWO_PI;

    diff = @xmag - @newXmag

    if (diff.abs >  0.01)
      @xmag -= diff/4.0
    end

    diff = @ymag - @newYmag
    if (diff.abs >  0.01) 
      @ymag -= diff/4.0
    end

    rotateX -@ymag
    rotateY -@xmag

    scale(50)
    begin_shape(QUADS)

    fill(0, 1, 1); vertex(-1,  1,  1)
    fill(1, 1, 1); vertex( 1,  1,  1)
    fill(1, 0, 1); vertex( 1, -1,  1)
    fill(0, 0, 1); vertex(-1, -1,  1)

    fill(1, 1, 1); vertex( 1,  1,  1)
    fill(1, 1, 0); vertex( 1,  1, -1)
    fill(1, 0, 0); vertex( 1, -1, -1)
    fill(1, 0, 1); vertex( 1, -1,  1)

    fill(1, 1, 0); vertex( 1,  1, -1)
    fill(0, 1, 0); vertex(-1,  1, -1)
    fill(0, 0, 0); vertex(-1, -1, -1)
    fill(1, 0, 0); vertex( 1, -1, -1)

    fill(0, 1, 0); vertex(-1,  1, -1)
    fill(0, 1, 1); vertex(-1,  1,  1)
    fill(0, 0, 1); vertex(-1, -1,  1)
    fill(0, 0, 0); vertex(-1, -1, -1)

    fill(0, 1, 0); vertex(-1,  1, -1)
    fill(1, 1, 0); vertex( 1,  1, -1)
    fill(1, 1, 1); vertex( 1,  1,  1)
    fill(0, 1, 1); vertex(-1,  1,  1)

    fill(0, 0, 0); vertex(-1, -1, -1)
    fill(1, 0, 0); vertex( 1, -1, -1)
    fill(1, 0, 1); vertex( 1, -1,  1)
    fill(0, 0, 1); vertex(-1, -1,  1)

    end_shape
    pop_matrix
  end

end

JFrame = javax.swing.JFrame
frame = JFrame.new "RGB Cube"
applet = Sketch.new
frame.content_pane.add applet
frame.default_close_operation = JFrame::EXIT_ON_CLOSE
applet.init
frame.pack
frame.visible = true

Exception in thread "Animation Thread" processing/core/PApplet.java:1013:in `size': processing.core.PApplet$RendererChangeException: null (NativeException)
	from processing/core/PApplet.java:959:in `size'
	from sun/reflect/NativeMethodAccessorImpl.java:-2:in `invoke0'
	from sun/reflect/NativeMethodAccessorImpl.java:39:in `invoke'
	from sun/reflect/DelegatingMethodAccessorImpl.java:25:in `invoke'
	from java/lang/reflect/Method.java:592:in `invoke'
	from org/jruby/javasupport/JavaMethod.java:302:in `invokeWithExceptionHandling'
	from org/jruby/javasupport/JavaMethod.java:263:in `invoke'
	from org/jruby/java/invokers/InstanceMethodInvoker.java:72:in `call'
	 ... 11 levels...
	from processing/core/PApplet.java:1328:in `run'
	from java/lang/Thread.java:613:in `run'
	from :1
Complete Java stackTrace
processing.core.PApplet$RendererChangeException
	at processing.core.PApplet.size(PApplet.java:1013)
	at processing.core.PApplet.size(PApplet.java:959)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:592)
	at org.jruby.javasupport.JavaMethod.invokeWithExceptionHandling(JavaMethod.java:302)
	at org.jruby.javasupport.JavaMethod.invoke(JavaMethod.java:263)
	at org.jruby.java.invokers.InstanceMethodInvoker.call(InstanceMethodInvoker.java:72)
	at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:318)
	at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:197)
	at test.method__1$RUBY$setup(test.rb:9)
	at testInvokermethod__1$RUBY$setupFixed0.call(test#setup)
	at testInvokermethod__1$RUBY$setupFixed0.call(test#setup)
	at org.jruby.internal.runtime.methods.DynamicMethod.call(DynamicMethod.java:138)
	at org.jruby.RubyClass.finvoke(RubyClass.java:511)
	at org.jruby.javasupport.util.RuntimeHelpers.invoke(RuntimeHelpers.java:419)
	at org.jruby.javasupport.proxy.JavaProxyConstructor$2.invoke(JavaProxyConstructor.java:230)
	at org.jruby.proxy.processing.core.PApplet$Proxy0.setup(Unknown Source)
	at processing.core.PApplet.handleDraw(PApplet.java:1403)
	at processing.core.PApplet.run(PApplet.java:1328)
	at java.lang.Thread.run(Thread.java:613)
	...internal jruby stack elided...
	from processing.core.PApplet.size(PApplet.java:959)
	from sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	from sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	from sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	from java.lang.reflect.Method.invoke(Method.java:592)
	from org.jruby.javasupport.JavaMethod.invokeWithExceptionHandling(JavaMethod.java:302)
	from org.jruby.javasupport.JavaMethod.invoke(JavaMethod.java:263)
	from org.jruby.java.invokers.InstanceMethodInvoker.call(InstanceMethodInvoker.java:72)
	from org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:318)
	from org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:197)
	from test.method__1$RUBY$setup(test.rb:9)
	from testInvokermethod__1$RUBY$setupFixed0.call(test#setup)
	from testInvokermethod__1$RUBY$setupFixed0.call(test#setup)
	from org.jruby.internal.runtime.methods.DynamicMethod.call(DynamicMethod.java:138)
	from org.jruby.RubyClass.finvoke(RubyClass.java:511)
	from org.jruby.javasupport.util.RuntimeHelpers.invoke(RuntimeHelpers.java:419)
	from org.jruby.javasupport.proxy.JavaProxyConstructor$2.invoke(JavaProxyConstructor.java:230)
	from org.jruby.proxy.processing.core.PApplet$Proxy0.setup(Unknown Source)
	from processing.core.PApplet.handleDraw(PApplet.java:1403)
	from processing.core.PApplet.run(PApplet.java:1328)
	from java.lang.Thread.run(Thread.java:613)