QQuickItem drag&drop event handlers do not have source set

I've create custom QQuickItem and re-implemented

dragEnterEvent(QDragEnterEvent *event)

dragLeaveEvent(QDragLeaveEvent *event)

dragMoveEvent(QDragMoveEvent *event)

dropEvent(QDropEvent *event)

In all the cases when I receive event the event->source() is null object. There is no way to determine which object was dropped. 

I looked at the DropArea code and it seems it is using something called QQuickDragMimeData which is private and can not be directly used in custom QQuickItem. 

I also checked that widgets use QDragManager to set the source for drop events. However this dropmanager is not either used in declarative.

Please do provide a way to access source of the events if available.