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