@Test
    public void testReturnTypes() {
        assertEquals("test", __.__("TEST").toLower().next());
        assertArrayEquals(new String[]{"hello", "test", "no.123", null, ""},
                __.__("hElLo", "TEST", "NO.123", null, "").toLower().toList().toArray());
    }
@author Yang Xia (http://github.com/xiazcy)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/ToLowerGlobalStepTest.java