title: Cannot write to containerURLForSecurityApplicationGroupIdentifier?
body: <p>In the following example, I get no errors on write, but while reading, the data length is 0. Why can't I write to the shared container?</p>
  
  <pre><code>+ (UIImage *)read {
      NSData *data = [NSData dataWithContentsOfFile:[self getPath]];
      NSLog(@"Data length: %d", data.length);
      UIImage *image = [UIImage imageWithContentsOfFile:[self getPath]];
      NSLog(@"%@", image);
      return image;
  }
  
  + (void)write:(UIImage *)image {
      NSString *pngFilePath = [self getPath];
      NSData *data1 = [NSData dataWithData:UIImagePNGRepresentation(image)];
      [data1 writeToFile:pngFilePath atomically:YES];
  }
  
  + (NSString *)getPath {
      NSURL *containerUrl = [[NSFileManager defaultManager] containerURLForSecurityApplicationGroupIdentifier:@"group.me.app"];
      NSString *pngFilePath = [[containerUrl absoluteString] stringByAppendingPathComponent:@"current.png"];
  
      NSLog(@"%@", pngFilePath);
      return pngFilePath;
  }
  </code></pre>