default List<String> invalidIndexRequiredFields(final Map<String, Object> source) {
        final RequiredValidator requiredValidator = new RequiredValidator();
        return split(getIndexAdminRequiredFields(), ",").get(stream -> stream.filter(StringUtil::isNotBlank)
                .map(String::trim)
                .filter(s -> !requiredValidator.isValid(source.get(s), null))
                .collect(Collectors.toList()));
    }