Converts the object to KAF (if it is NAF)

def to_kaf(self):
        """
        Converts the object to KAF (if it is NAF)
        """
        if self.type == 'NAF':
            self.type = 'KAF'
            for node in self.__get_node_terms():
                node.set('cid', node.get('id'))
                del node.attrib['id']