 
 public class Events {
 
-    public class func list(queue: dispatch_queue_t = dispatch_get_main_queue(), callback: EventList) {
+    public class func list(queue: dispatch_queue_t? = nil, callback: EventList) {
         /* Configure session, choose between:
         * defaultSessionConfiguration
         * ephemeralSessionConfiguration

            if let error = error {
                // Failure
                print("URL Session Task Failed: \(error.localizedDescription)");
                dispatch_sync(queue) {
                    callback(events: nil)
                }
            }
            else {

                let statusCode = (response as! NSHTTPURLResponse).statusCode
                print("URL Session Task Succeeded: HTTP \(statusCode)")
//        let json = try! NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as? NSDictionary

                let events = [""]

                // Call back on same queue if none specified
                if queue == nil {
                    callback(events: events)
                }
                else {
                    dispatch_sync(queue!) {
                        callback(events: events)
                    }
                }
            }
        })
