     *  @param label (can be nil)
     */
     init(serial label: String?) {
-        if label {
+        if label != nil {
             dispatchQueue = dispatch_queue_create(label!, DISPATCH_QUEUE_SERIAL)
         }
         else {

    *  @param label (can be nil)
    */
    init(concurrent label: String?) {
        if label {
            dispatchQueue = dispatch_queue_create(label!, DISPATCH_QUEUE_CONCURRENT)
        }
        else {

    *
    *  @return
    */
    class func once(predicate: UnsafeMutablePointer<dispatch_once_t>, closure: GCDClosure) {
        dispatch_once(predicate, closure)
    }
}