After checking the source code of groovyx.javafx.SceneGraphBuilder. Mixing a griffon view + swing toolkit + javafx, the way I expected it to be=>ERROR

griffon+swing+javafx

package testmixfx

import javafx.embed.swing.JFXPanel
import groovyx.javafx.GroovyFX
import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Scene;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;
import groovyx.javafx.SceneGraphBuilder;


JFXPanel jfxPanel = new JFXPanel();
def DEFAULT_URL = "http://www.yahoo.com"


application(title: 'testmixfx',
  preferredSize: [320, 240],
  pack: true,
  locationByPlatform: true,
  iconImage:   imageIcon('/griffon-icon-48x48.png').image,
  iconImages: [imageIcon('/griffon-icon-48x48.png').image,
               imageIcon('/griffon-icon-32x32.png').image,
               imageIcon('/griffon-icon-16x16.png').image]) {
    // add content here    
    panel(id:"myPanel",preferredSize: new Dimension(800,400)){
      migLayout(layoutConstraints: 'fill')
      label('Content Goes Here',constraints:"wrap")
      widget(jfxPanel)
    }    

    //http://svn.codehaus.org/gmod/groovyfx/trunk/groovyfx/src/demo/groovy/SwingDemo.groovy
    //http://fxexperience.com/2011/07/interview-with-the-developers-behind-groovyfx/    
   GroovyFX.start {
     def sg = new groovyx.javafx.SceneGraphBuilder(true);
     jfxPanel.scene = sg.scene(width: 800, height: 400) {
         webEngine = webEngine(location: DEFAULT_URL)
         webView(engine: webEngine)
     }
   } //-->ERROR: No signature of method: java.lang.Object.webEngine() is applicable for argument types: (java.util.LinkedHashMap, null) values: [[location:http://www.yahoo.com], null]

}