private Set<String> splitGroupConcat(final String str) {
        if (NullSafe.isEmptyString(str)) {
            return Collections.emptySet();
        } else {
            // Could potentially be loads of parts so truncate to a sensible number.
            // MySQL will also truncate the length of the returned string to
            // 1024 (or the value of param 'group_concat_max_len')
            final String[] parts = GROUP_CONCAT_DELIMITER_PATTERN.split(str);
            return NullSafe.stream(parts)
                    .limit(SelectionSummary.MAX_GROUP_CONCAT_PARTS)
                    .collect(Collectors.toSet());
        }
    }
@return True if any term in any rule expression uses at least one of {@code fields}.
stroom-meta/stroom-meta-impl-db/src/main/java/stroom/meta/impl/db/MetaDaoImpl.java