assertEquals("\"boolKey\":\"true\"", buf.toString());
    }

    // Test append method with Date value (other object type)
    @Test
    public void test_append_dateValue() {
        StringBuilder buf = new StringBuilder();
        Date date = new Date(1609459200000L);
        Supplier<Object> supplier = () -> date;

        monitorTarget.append(buf, "dateKey", supplier);