[Swift] Convert AnyObject to JSON String

AnyObjectToJSONString

class LINJSONHelper {
    class func jsonStringWithObject(obj: AnyObject) -> String? {
        var error: NSError?
        let jsonData  = NSJSONSerialization.dataWithJSONObject(obj, options: NSJSONWritingOptions(0), error: &error)
        if error != nil {
            println("Error creating JSON data: \(error!.description)");
            return nil
        }
        
        return NSString(data: jsonData, encoding: NSUTF8StringEncoding)
    }
}