setRequiredError not working

I was just going through the demo and was noticing that the add/edit form fails silently when you don’t enter a zip code.

So I looked into this and found the method “setRequiredError”.
However when I add this method, I still get no feedback when hitting submit.

                if (propertyId.equals("postalCode")) {
                    TextField tf = (TextField) field;
                     * We do not want to display "null" to the user when the
                     * field is empty

                    /* Add a validator for postalCode and make it required */
                    tf.addValidator(new RegexpValidator("[1-9]
                        "Postal code must be a five digit number and cannot start with a zero."));
                    tf.setRequiredError("This should displaying when hitting submit");

Which demo? Can you provide a link?