@Test
    public void test_get_booleanValues() {
        String trueKey = "boolean.true";
        String falseKey = "boolean.false";

        System.setProperty(Constants.FESS_CONFIG_PREFIX + trueKey, "true");
        System.setProperty(Constants.FESS_CONFIG_PREFIX + falseKey, "false");

        try {
            String trueValue = fessConfig.get(trueKey);
            assertEquals("true", trueValue);

        assertEquals("first", DocumentUtil.getValue(doc, "key", String.class));

        List<String> numList = Arrays.asList("123", "456", "789");
        doc.put("numKey", numList);
        assertEquals(Integer.valueOf(123), DocumentUtil.getValue(doc, "numKey", Integer.class));
    }

    @Test
    public void test_first_element_from_string_array() {
        Map<String, Object> doc = new HashMap<>();