Returns any drag information that will be used from this chart item.
        
        :return     <QMimeData> || None

def dragData(self, x=None, y=None):
        """
        Returns any drag information that will be used from this chart item.
        
        :return     <QMimeData> || None
        """
        # look for specific drag information for this item
        first  = (x, y)
        second = (x, None)
        third  = (None, y)
        fourth = (None, None)
        
        for key in (first, second, third, fourth):
            data = self._dragData.get(key)
            if data:
                return data
        
        return None