@Override
        public void clear() {
            final Map<String,String> originalMap = new HashMap<>(); // copy to be used by event handling.
            for (Entry<K,V> entry : delegate) {
                if (entry.getKey() instanceof String && entry.getValue() instanceof String) {
                    originalMap.put((String) entry.getKey(), (String) entry.getValue());
                }
            }
            delegate.clear();
            deleteAllProperties(originalMap);
        }
Removes all the elements in the set, and applies the
corresponding update to the database.
xmppserver/src/main/java/org/jivesoftware/openfire/group/DefaultGroupPropertyMap.java