.map(String::trim)
                .filter(s -> !requiredValidator.isValid(source.get(s), null))
                .collect(Collectors.toList()));
    }

    default boolean isNonEmptyValue(final Object value) {
        final RequiredValidator requiredValidator = new RequiredValidator();
        return requiredValidator.isValid(value, null);
    }

    String getCrawlerDocumentSpaceChars();