RenderData data = new RenderData();
        RenderDataUtil.register(data, "key1", null);
        assertNull(data.getDataMap().get("key1"));
    }

    @Test
    public void test_register_string() {
        RenderData data = new RenderData();
        RenderDataUtil.register(data, "key1", "test value");
        assertEquals("test value", data.getDataMap().get("key1"));