@Test
    @LoadGraphWith(MODERN)
    public void g_V_hasLabelXnull_personX() {
        final Traversal<Vertex, Vertex> traversal = get_g_V_hasLabelXnull_personX();
        printTraversalForm(traversal);
        final List<Vertex> vertices = traversal.toList();
        assertEquals(4, vertices.size());
        assertThat(vertices.stream().allMatch(v -> v.label().equals("person")), is(true));
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/filter/HasTest.java