Photo Bomber keep crushing when instagram login is cancel

hi Photo Bomber keep crashing when Instagram login is cancel , i guess it crashing due to the response object , i am a bit confused please help

UINavigationBar *navigationBar = navigationController.navigationBar; navigationBar.barTintColor = [UIColor colorWithRed:232.0 / 255.0 green:129.0 / 255.0 blue:91.0 / 255.0 alpha:1.0]; navigationBar.barStyle = UIBarStyleBlackOpaque; navigationBar.tintColor = [UIColor whiteColor]; [self.collectionView registerClass:[THPhotoCell class] forCellWithReuseIdentifier:@"photo"]; self.collectionView.backgroundColor = [UIColor blackColor]; NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults]; self.accessToken = [userDefaults objectForKey:@"accessToken"];

if (self.accessToken == nil) {
    [SimpleAuth authorize:@"instagram" options:@{@"scope": @[@"likes"]} completion:^(NSDictionary *responseObject, NSError *error) {

        self.accessToken = responseObject[@"credentials"][@"token"];

        [userDefaults setObject:self.accessToken forKey:@"accessToken"];
        [userDefaults synchronize];

        [self refresh];
    }];
} else {
    [self refresh];
}
[self refresh];

[self refresh];}

• (void)refresh { if (self.loading) { return; }

  self.loading = YES;

  NSURLSession *session = [NSURLSession sharedSession];

  // You can change the hashtag here to make your very own photo browser app! NSString *urlString = [[NSString alloc] initWithFormat:@"https://api.instagram.com/v1/tags/photobomber/media/recent?access_token=%@&count=500", self.accessToken];

  NSURL *url = [[NSURL alloc] initWithString:urlString]; NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url]; NSURLSessionDownloadTask *task = [session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {

  NSData *data = [[NSData alloc] initWithContentsOfURL:location];
  NSDictionary *responseDictionary = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
  
  self.photos = [responseDictionary valueForKeyPath:@"data"];
  
  dispatch_async(dispatch_get_main_queue(), ^{
      [self.collectionView reloadData];
      self.loading = NO;
  });
  

  }]; [task resume]; }