monitorTarget.append(buf, "errorKey", supplier);
        assertEquals("\"errorKey\":null", buf.toString());
    }

    // Test append method with Boolean value (other object type)
    public void test_append_booleanValue() {
        StringBuilder buf = new StringBuilder();
        Supplier<Object> supplier = () -> Boolean.TRUE;

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