Junit trying to confirm Null is returned

I have this extra credit assignment that makes me do junit test but I don't understand how I can make my test for getDestinations return null. So I have this methods and variable:

private final Point3D destination = new Point3D();

public Point3D getDestination() {
        if (destination == null) {
            return null;
        }
        return new Point3D(destination);
    }


public final void setDestination(Point3D aPoint) throws InvalidDataException {
        if (aPoint == null) {
            throw new InvalidDataException("Null Point3D sent to setDestination(Point3D)");
        }
        setDestination(aPoint.getX(), aPoint.getY(), aPoint.getZ());
    }

I'm trying to make netbeans know that I when I test for destination = null it returns null.

Hers my test so far:

   public void testGetDestination(){
        testPoint3D = new Point3D(4.0, 5.0, 6.0);
        Point3D p = testMovable.getDestination();
        assertEquals(p, testPoint3D);
        assertNotNull(p); 
    }
   public void testSetDestination_Point3D() throws Exception {
        Point3D newPoint = new Point3D(0.0, 0.0, 0.0);
        testMovable.setDestination(newPoint);
        Point3D p = new Point3D();
        assertNotNull(p);
        assertEquals(p, newPoint);
        assertNotSame(p, newPoint);
        p = null;
        try{
            testMovable.setDestination(p);
            fail("Null Point3D sent to setDestination(Point3D)");
        }catch(InvalidDataException ex){ 
            assertEquals(ex.getMessage(),"Null Point3D sent to setDestination(Point3D)");
        }
    }

but as you can see I can't really invoke a null without having it to fail/caught by exceptions.

Is there a way to go about this?