Spot the bug...

Transformer.java

public class Transformer {

   private LegacyScreenImpl screen;

   public LegacyScreenImpl asLegacyScreen(Model model, String previousScreen) {
     screen = asLegacyScreen(model);
     screen.setPreviousScreenName(previousScreen);
     return screen;
   }

    public LegacyScreenImpl asLegacyScreen(Model model) {
       screen = new LegacyScreenImpl();
       if(model != null) {
           screen.setModel(getScreenModel(model));
           screen.setTitle(model.getTitleValue()); 
       }
       return screen;
    }
}