我想你想要这个：

if( false == o.empty() )
{
    do 
    {
        std::cout << "key: " << key << " val: " << value << std::endl;
    }while (o.getNextElement(key, value));
}

在获得元素之前判断它是否为null。

To judge whether it is 'null', before you get elements.