static Set<CIKey> commonKeys() {
        //noinspection Java9CollectionFactory // GWT :-(
        return Collections.unmodifiableSet(new HashSet<>(KEY_TO_COMMON_CIKEY_MAP.values()));
    }
@return The set of all common {@link CIKey}s
stroom-util-shared/src/main/java/stroom/util/shared/string/CIKeys.java