http://wikis.sun.com/display/JavaFxCodeConv/Home

Now the CustomNode item in the Applications category looks like:
-------------------------------------------------------------
class MyCustomNode extends CustomNode {

    public override function create(): Node {
        return Group {
                    content: []
                };
         }

}
-------------------------------------------------------------

According to the Coding Conventions for the JavaFX Language
the return type and return keyword should be omitted  in the code
http://wikis.sun.com/display/JavaFxCodeConv/Home

The updated code can look like:
-------------------------------------------------------------
import javafx.scene.Group;
import javafx.scene.CustomNode;

class MyCustomNode extends CustomNode {

    public override function create() {
        Group {
            content: []
        }
    }

}
-------------------------------------------------------------