private DropHandler getDropHandler(DnDEvent event) {
    if (event == null) return null;
    DnDAction action = event.getAction();
    if (action == null) return null;
    int id = action.getActionId();
    if (id == DnDConstants.ACTION_COPY) return createCopyHandler();
    if (id != DnDConstants.ACTION_COPY_OR_MOVE && id != DnDConstants.ACTION_MOVE) return null;
    return createMoveHandler();
  }
private DropHandler getDropHandler(DnDEvent event)