@SuppressWarnings("NullableProblems")
    @Override
    public Set<String> keySet() {
        final Set<String> rtnSet = new HashSet<>();
        for (final CIString entry : realMap.keySet()) {
            rtnSet.add(entry.key);
        }
        return rtnSet;
    }
String hash map that does not care about key case.
stroom-util/src/main/java/stroom/util/CIStringHashMap.java