private void validateFormat(JsonNode node, List<ErrorMessage> results) {
        if (format != null) {
            FormatValidator formatValidator = formatValidators.get(format);
            if (formatValidator!= null && !formatValidator.isValid(node)) {
                results.add(new ErrorMessage("", "Value '" + node.textValue() + "' is not a valid " + format));
            }
        }
    }