No drop with NSDraggingSession

In the "mouseDown" (or MouseDreagged) code below Enclosure is a NSView subclass. xcode report 2 warnings:

pb_item setDataProvider:self forTypes:[NSArray arrayWithObjects:NSPasteboardTypeTIFF, NSPasteboardTypePDF, @"LN_PboardType", nil]];

Sending 'Enclosure *' to parameter of incompatible type 'id _Nonnull'

NSDraggingSession *draggingSession = [self beginDraggingSessionWithItems:[NSArray arrayWithObject:drag_item] event:drag_event source:self];

Sending 'Enclosure *' to parameter of incompatible type 'id _Nonnull'

The application fail at:

drag_item = [[NSDraggingItem alloc] initWithPasteboardWriter:pb_item];

Pasteboard item data provider <Enclosure: 0x7f849ec74e70> must conform to NSPasteboardItemDataProviderProtocol [General] There are 0 items on the pasteboard, but 1 drag images. There must be 1 draggingItem per pasteboardItem.

However if in the line of code above "pb_item" is replaced by "drag_image" drag work fine (but without drop). The z_drag image follow the mouse correctly and "endedAtPoint" is called when the mouse button is released.

Where is the error ?

Any suggestion will be appreciate...

BigSur, xcode 12.4

- (void)mouseDown:(NSEvent *)drag_event  /* or mouseDragged:(NSEvent *)drag_event */
	{
	NSImage *drag_image;
	NSPoint drag_position;
    NSDraggingItem *drag_item;
	NSPasteboardItem *pb_item;

	pb_item = [[NSPasteboardItem alloc] init];
	[pb_item setDataProvider:self forTypes:[NSArray arrayWithObjects:NSPasteboardTypeTIFF, NSPasteboardTypePDF, @"LN_PboardType", nil]];

	drag_image = [NSImage imageNamed:@"z_drag.jpg"];

	drag_item = [[NSDraggingItem alloc] initWithPasteboardWriter:pb_item];
	drag_position = [self convertPoint:[drag_event locationInWindow] fromView:nil];
	drag_position.x -= [drag_image size].width/2;
	drag_position.y -= [drag_image size].height/2;
	[drag_item setDraggingFrame:NSMakeRect(drag_position.x, drag_position.y, drag_image.size.width, drag_image.size.height) contents:drag_image];

	NSDraggingSession *draggingSession = [self beginDraggingSessionWithItems:[NSArray arrayWithObject:drag_item] event:drag_event source:self];
	[draggingSession setAnimatesToStartingPositionsOnCancelOrFail:YES];
	[draggingSession setDraggingFormation:NSDraggingFormationNone];
	}

- (NSDragOperation)draggingSession:(NSDraggingSession *)session sourceOperationMaskForDraggingContext:(NSDraggingContext)context
	{
	switch (context)
		{
		case NSDraggingContextWithinApplication:
			return NSDragOperationCopy;

		case NSDraggingContextOutsideApplication:
			return NSDragOperationMove;
		}

	return NSDragOperationNone;
	}

- (void)draggingSession:(NSDraggingSession *)session endedAtPoint:(NSPoint)screenPoint operation:(NSDragOperation)operation
	{
	NSPoint mouse_point;

	mouse_point = [session draggingLocation];

	switch (operation)
		{
		case NSDragOperationDelete:
            break;
		default:
			break;
		}
	}