writePromiseTo not called on macOS 11.0 Beta (20A5395g)

I want to implement drag&drop of an entry in an NSTableView to a folder in Finder.

Here is my code of the controller:

Code Block 
override func viewDidLoad() {
  super.viewDidLoad()
  self.tableView.setDraggingSourceOperationMask(.copy, forLocal: false)
}
func tableView(_ tableView: NSTableView, 	pasteboardWriterForRow row: Int) -> NSPasteboardWriting? {
	return NSFilePromiseProvider(fileType: kUTTypeJPEG as String, delegate: self)
    }
func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, fileNameForType fileType: String) -> String {
    return "test.jpg"
}
func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, writePromiseTo url: URL, completionHandler: @escaping (Error?) -> Void) {
   print("never called")
}

The method filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, fileNameForType fileType: String) is called.

But filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, writePromiseTo url: URL, completionHandler: @escaping (Error?) -> Void) is never called.

I am using Xcode 12.2 beta 3 (12B5035g).

Do you have similar problems with drag&drop?

Thanks,
Dirk