* @param key   Key to associate with value.
     * @param value Value to place into group/collection.
     * @return value previously associated with the provided key
     */
    public V put( G group, K key, V value ) {
        Node<K, V> ret = putKeyNode( group, key, value );
        if( ret == null ) { return null; }

        return ret.mValue;
    }