assertEquals("hello_world", DocumentUtil.encodeUrl("hello_world"));
        assertEquals("hello.world", DocumentUtil.encodeUrl("hello.world"));
    }

    @Test
    public void test_encodeUrl_empty_and_null() {
        assertEquals("", DocumentUtil.encodeUrl(""));
        try {
            DocumentUtil.encodeUrl(null);
            fail("Should throw NullPointerException");