If you do:

        Object r = new Object();
        GraphLayout gl1 = GraphLayout.parseInstance(r);
        GraphLayout gl2 = GraphLayout.parseInstance(r, r);

...then this would unexpectedly fail:

        Assert.assertEquals(gl1.totalCount(), gl2.totalCount());
        Assert.assertEquals(gl1.totalSize(), gl2.totalSize());

This is because GraphWalker counts these separate roots as separate objects, which should not happen.