Cell Clickable Renderer with vCheckBox widget

Hi,
Using this info from the book almost everything works fine, when I click an unchecked box, it turns checked and the checkbox.setText("X") sets the text, and when I uncheck the box, it does, but the text does not gets cleared  checkbox.setText("") or checkbox.setText(null) don't work. please help me.
 
server side renderer

addClickListener(new RendererClickListener() {
            /**
             * 
             */
            private static final long serialVersionUID = 7908980496657581489L;

            @Override
            public void click(RendererClickEvent event) {
                Grid grid = getParentGrid();
                Object itemId = event.getItemId();
                Object propertyId = event.getPropertyId();
                Container.Indexed containerDataSource = grid.getContainerDataSource();
                Property<String> itemProperty = containerDataSource.getItem(itemId).getItemProperty(propertyId);
                grid.setImmediate(true);
                logger.log(Level.INFO, "A itemProperty = " + itemProperty.getValue());
                
                String[] vals = itemProperty.getValue().split("-");
                if(vals[0].equals(getSession().getAttribute("user").toString())) {
                    itemProperty.setValue("0-");
                } else if (vals[0].equals("0")) {
                    itemProperty.setValue(getSession().getAttribute("user").toString().concat("-").concat(getSession().getAttribute("user").toString()));
                }

                logger.log(Level.INFO, "B itemProperty = " + itemProperty.getValue());
            }
        });

client side renderer
    

VCheckBox chkBox;

    @Override
    public VCheckBox createWidget() {
        VCheckBox b = GWT.create(VCheckBox.class);
        b.addClickHandler(this);
        b.setStylePrimaryName("v-checkbox");
        b.setEnabled(false);
        return b;
    }

    @Override
    public void render(RendererCellReference cell, String usuario, VCheckBox checkBox) {
        String[] usr = usuario.split("-");
        chkBox = checkBox;
        setbox(usr);
    }
    
    @Override
    public void render(RendererCellReference cell, String data) {
        String[] usr = data.split("-");
        setbox(usr);
    }
    
    void setbox(String[] usr) {
        chkBox.setText("");
        chkBox.setTitle("");
        chkBox.setValue(!usr[0].equals("0"), false);
        if(chkBox.getValue()) {
            chkBox.setText(usr[0]);
            chkBox.setTitle(usr[1]);
        }
    }

sorry guys, i was compiling the wrong widgetset