Program: 277
Project: 277
Buggy source:
@Override public void initialise(){
  zoomSlider=find("String_Node_Str",UISlider.class);
  if (zoomSlider != null) {
    zoomSlider.setValue(2f);
    zoomSlider.setUiSliderOnChangeTriggeredListener(this);
  }
  final UIDropdownScrollable worldsDropdown=find("String_Node_Str",UIDropdownScrollable.class);
  worldsDropdown.bindSelection(new Binding<String>(){
    @Override public String get(){
      return selectedWorld;
    }
    @Override public void set(    String value){
      selectedWorld=value;
      try {
        if (findWorldByName().getWorldGenerator() == null) {
          worldGenerator=WorldGeneratorManager.createWorldGenerator(findWorldByName().getWorldGeneratorInfo().getUri(),context,environment);
          findWorldByName().setWorldGenerator(worldGenerator);
        }
 else {
          worldGenerator=findWorldByName().getWorldGenerator();
        }
        if (worldGenerator.getWorldSeed() == null) {
          worldGenerator.setWorldSeed(createSeed(selectedWorld));
        }
        previewGen=new FacetLayerPreview(environment,worldGenerator);
        updatePreview();
      }
 catch (      UnresolvedWorldGeneratorException e) {
        e.printStackTrace();
      }
    }
  }
);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> {
    worldGenerator.setWorldSeed(createSeed(selectedWorld));
    updatePreview();
  }
);
  StartPlayingScreen startPlayingScreen=getManager().createScreen(StartPlayingScreen.ASSET_URI,StartPlayingScreen.class);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> {
    startPlayingScreen.setTargetWorld(worldList,findWorldByName(),texture,context);
    triggerForwardAnimation(startPlayingScreen);
  }
);
  WorldSetupScreen worldSetupScreen=getManager().createScreen(WorldSetupScreen.ASSET_URI,WorldSetupScreen.class);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> {
    try {
      if (!selectedWorld.isEmpty()) {
        worldSetupScreen.setWorld(context,findWorldByName());
        triggerForwardAnimation(worldSetupScreen);
      }
 else {
        getManager().pushScreen(MessagePopup.ASSET_URI,MessagePopup.class).setMessage("String_Node_Str","String_Node_Str");
      }
    }
 catch (    UnresolvedWorldGeneratorException e) {
      e.printStackTrace();
    }
  }
);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> triggerBackAnimation());
}

Fixed version (ground truth):
@Override public void initialise(){
  zoomSlider=find("String_Node_Str",UISlider.class);
  if (zoomSlider != null) {
    zoomSlider.setValue(2f);
    zoomSlider.setUiSliderOnChangeTriggeredListener(this);
  }
  final UIDropdownScrollable worldsDropdown=find("String_Node_Str",UIDropdownScrollable.class);
  worldsDropdown.bindSelection(new Binding<String>(){
    @Override public String get(){
      return selectedWorld;
    }
    @Override public void set(    String value){
      selectedWorld=value;
      try {
        if (findWorldByName(selectedWorld).getWorldGenerator() == null) {
          worldGenerator=WorldGeneratorManager.createWorldGenerator(findWorldByName(selectedWorld).getWorldGeneratorInfo().getUri(),context,environment);
          findWorldByName(selectedWorld).setWorldGenerator(worldGenerator);
        }
 else {
          worldGenerator=findWorldByName(selectedWorld).getWorldGenerator();
        }
        if (worldGenerator.getWorldSeed() == null) {
          worldGenerator.setWorldSeed(createSeed(selectedWorld));
        }
        previewGen=new FacetLayerPreview(environment,worldGenerator);
        updatePreview();
      }
 catch (      UnresolvedWorldGeneratorException e) {
        e.printStackTrace();
      }
    }
  }
);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> {
    worldGenerator.setWorldSeed(createSeed(selectedWorld));
    updatePreview();
  }
);
  StartPlayingScreen startPlayingScreen=getManager().createScreen(StartPlayingScreen.ASSET_URI,StartPlayingScreen.class);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> {
    startPlayingScreen.setTargetWorld(worldList,findWorldByName(selectedWorld),texture,context);
    triggerForwardAnimation(startPlayingScreen);
  }
);
  WorldSetupScreen worldSetupScreen=getManager().createScreen(WorldSetupScreen.ASSET_URI,WorldSetupScreen.class);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> {
    try {
      if (!selectedWorld.isEmpty()) {
        worldSetupScreen.setWorld(context,findWorldByName(selectedWorld));
        triggerForwardAnimation(worldSetupScreen);
      }
 else {
        getManager().pushScreen(MessagePopup.ASSET_URI,MessagePopup.class).setMessage("String_Node_Str","String_Node_Str");
      }
    }
 catch (    UnresolvedWorldGeneratorException e) {
      e.printStackTrace();
    }
  }
);
  WidgetUtil.trySubscribe(this,"String_Node_Str",button -> triggerBackAnimation());
}