libGDX DragAndDropText.java is broken, looking for another example

I want to drag and drop TextButtons to designated targets. Searching this site, DragAndDropTest.java on libgdx's testing github is cited as an example to to start from. Implementing the flow described in the test, I received this error:

Exception in thread "main" java.lang.NullPointerException
at com.badlogic.gdx.scenes.scene2d.utils.DragAndDrop$1.drag(DragAndDrop.java:111)
at com.badlogic.gdx.scenes.scene2d.utils.DragListener.touchDragged(DragListener.java:61)
at com.badlogic.gdx.scenes.scene2d.InputListener.handle(InputListener.java:62)
at com.badlogic.gdx.scenes.scene2d.Stage.touchDragged(Stage.java:315)
at com.badlogic.gdx.InputEventQueue.drain(InputEventQueue.java:89)
at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Input.update(Lwjgl3Input.java:205)
at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Window.update(Lwjgl3Window.java:390)
at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Application.loop(Lwjgl3Application.java:137)
at com.badlogic.gdx.backends.lwjgl3.Lwjgl3Application.<init>(Lwjgl3Application.java:111)
at com.b2tclient.lwjgl3.Lwjgl3Launcher.createApplication(Lwjgl3Launcher.java:17)
at com.b2tclient.lwjgl3.Lwjgl3Launcher.main(Lwjgl3Launcher.java:12)

Eventually I just tried to run the DragAndDropTest.java directly and received the same error. Anything from a fixed test, pointing out where I may have gone wrong in trying to run the test, or a different working example of drag and drop to study would all be helpful in moving forward.

Note that I also tried a different path when I struck out here in implementing Lee Stemkoski's DragAndDropActor class. While that did work, the flow I learned from doing so is only good for his BaseActor family, and the work of re-implementing Buttons and such on top of it doesn't seem like the right solution. I'll take from that effort confirmation that drag and drop itself is not broken, just the test.

I've ripped out all of the dragging methods and tracking variables from Stemkoski's DragAndDropActor, and placed them in .addListener() for each item I want to drag within my screen. Now that I've seen my draggables moving around the screen without crashing, I think I'll make a new DragListener extending from InputListener, as that seems like the way to encapsulate the logic (open to feedback). Anyway, it occurs to me that the DragAndDrop class found in the DragAndDropText is never referenced in Stemkoski's work, so he must have implemented his own parallel drag and drop functionality. So I take back what I said about knowing the drag and drop that comes with native libgdx works, however unlikely it would seem that it not.

While this is technically an example of drag and drop that still works compared to the oft-cited test class, I think any answer provided that uses the vanilla libgdx packages should be considered a superior one.

I've done something like that :

public class DragAndDropActorListener extends DragListener {
    private Actor actor;

    public DragAndDropActorListener(Actor actor) {
        this.actor = actor;
    }


    @Override
    public void drag(InputEvent event, float x, float y, int pointer) {
        this.actor.setY(event.getStageY());
        this.actor.setX(event.getStageX());
        super.drag(event, x, y, pointer);
    }

}

With actor the object to move. you could also a little Offset for center the object on the mouse