public synchronized void add(final StoredError storedError) {
        // Check to make sure we haven't seen this error before. If we have then
        // ignore it as we only want to store unique errors.
        if (uniqueErrorSet.add(storedError)) {
            errorList.add(storedError);
            errorCount.merge(storedError.getSeverity(), 1, Integer::sum);
        }
    }
Add all of the indicators from another map.
stroom-util-shared/src/main/java/stroom/util/shared/Indicators.java