private void evictCachedUserSharedGroups() {
        groupMetaCache.keySet().stream()
            .filter(key -> key.startsWith(GROUP_NAMES_KEY))
            .forEach(groupMetaCache::remove);
    }
Splits a comma-separated string of group name in a set of group names.
@param csv The comma-separated list. Cannot be null.
@return A set of group names.
xmppserver/src/main/java/org/jivesoftware/openfire/group/GroupManager.java