title: convert NSTaggedPointerString to NSString
body: <p>I had called an interface of Baidu to check id Number, however the value of Sex returned with <code>sex = M</code>, without "" around the <code>M</code> in JSON, when I use <code>NSString</code> in module to store it and then print the class name of this <code>sex</code> property, it printed as <code>NSTaggedPointerString</code>, I doubt how to convert it to a String to use it. Anyone have good ideas?</p>