@Test
    public void testReturnTypes() {
        assertEquals(Collections.emptyList(), __.__(Collections.emptyList()).reverse().next());
        assertEquals("tset", __.__("test").reverse().next());
        assertArrayEquals(new String[]{"dlrow olleh", "tset", "321.on", null, ""},
                __.inject("hello world", "test", "no.123", null, "").reverse().toList().toArray());
    }
@author Yang Xia (http://github.com/xiazcy)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/ReverseStepTest.java