Q:

LIBGDX 3D not working

So I am just starting off with the 3D part of LIBGDX.  I downloaded the latest nightly build and when I followed the tutorial I got a nullPointerException on a line(Which will mark in the code).  On the line has a nullPointer is this code
modelBatch.render(instance);

All the values for this line are there.  The instance has all its properties and pretty much everything else in my code does to.  Any ideas why I am getting a nullPointerException?  Thanks in advance. 
import com.badlogic.gdx. ApplicationListener;
import com.badlogic.gdx. Gdx;
import com.badlogic.gdx.graphics. Color;
import com.badlogic.gdx.graphics. GL10;
import com.badlogic.gdx.graphics. PerspectiveCamera;
import com.badlogic.gdx.graphics. VertexAttributes. Usage;
import com.badlogic.gdx.graphics.g3d. Model;
import com.badlogic.gdx.graphics.g3d. ModelBatch;
import com.badlogic.gdx.graphics.g3d. ModelInstance;
import com.badlogic.gdx.graphics.g3d.materials. ColorAttribute;
import com.badlogic.gdx.graphics.g3d.materials. Material;
import com.badlogic.gdx.graphics.g3d.utils. ModelBuilder;

public class threeDTest implements ApplicationListener {
public PerspectiveCamera camera;
public ModelBatch modelBatch;
public Model model;
public ModelInstance instance;

    @Override
    public void create() {
        camera =  new PerspectiveCamera(67, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        camera.position.set(10f, 10f, 10f);
        camera.lookAt(0, 0, 0);
        camera.near = 0.1f;
        camera.far = 300f;
        camera.update();

    ModelBuilder modelBuilder = new ModelBuilder();
    model = modelBuilder.createBox(5f, 5f, 5f, 
        new Material(ColorAttribute.createDiffuse(Color. GREEN)),
        Usage. Position | Usage. Normal);
    instance = new ModelInstance(model);
    }

    @Override
    public void resize(int width, int height) {

    }

    @Override
    public void render() {  
        Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

        modelBatch.begin(camera);//Begin Rendering
        modelBatch.render(instance);<--Null Pointer on this line
        modelBatch.end();//End Rendering
    }

@Override
public void pause() {

}

@Override
    public void resume() {

    }

    @Override
    public void dispose() {
        model.dispose();
    }

}

A:

Looking at you code you never construct (and dispose) the modelBatch instance.  Therefor the modelBatch will be null, causing the NPE you got. 
Add the following line in your create method:
modelBatch = new ModelBatch();

and the following line in your dispose method:
modelBatch.dispose();

