@Test
public void testOneNull() {

    Point3d bar = new Point3d(1.0, 5.0, 8.3);
    IDifference result = Point3dDifference.construct("Foo", null, bar);
    Assert.assertNotNull(result);
    result = Point3dDifference.construct("Foo", bar, null);
    Assert.assertNotNull(result);
}