UIContext.getSelection() always return null

value.setDefaultValue(new Callable<JavaResource>() {
 @Override
 public JavaResource call() throws Exception {   
    Object selected = builder.getUIContext().getSelection();
    if(selected != null && selected instanceof JavaResource) {
       return (JavaResource)selected;
    }
    return null;
 }
});

Object selected = builder.getUIContext().getInitialSelection().get();