@Override
    public V put(K key, V value) {
        if (value == null) { // treat null value as "remove"
            return remove(key);
        } else {
            return put(key, value, true);
        }
    }
Custom method to put properties into the map, optionally without
triggering persistence. This is used when the map is being 
initially loaded from the database.

@param key The property name
@param value The property value
@param persist True if the changes should be persisted to the database
@return The original value or null if the property did not exist
xmppserver/src/main/java/org/jivesoftware/openfire/group/DefaultGroupPropertyMap.java