public static String toAllowMessage(ValidationId id) {
        return "To allow this add <allow until='yyyy-mm-dd'>" + id + "</allow> to validation-overrides.xml" +
               ", see https://docs.vespa.ai/en/reference/validation-overrides.html";
    }
Returns the XML form of this, or null if it was not created by fromXml, nor is empty
config-model-api/src/main/java/com/yahoo/config/application/api/ValidationOverrides.java