JSON Data isn't being populated
===

I'm trying to write a Facebook Feed app for iOS, and I'm trying to use the JSON framework, to little effect. Whenever I run my code, I get the error "*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'data parameter is nil'". I'm using a feed from Flickr as a test/demonstration URL, as the Facebook URL is programmatically created using an Access Token request and appendToString:.

        NSURL *url2 = [NSURL URLWithString:@"www.flickr.com/services/feeds
                         /photos_public.gne?tags=punctuation,atsign&format=json"];
        NSData *data = [NSData dataWithContentsOfURL:url2];
        NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data 
                                                             options:kNilOptions 
                                                              error:nil];

I got this code from tutorials and previous StackOverflow questions and answers, so you won't be breaking my heart if it's wrong, or if you know of a better way to do this. Let me know if you need any more information.