'Reset an API callback to use a default handler.
:param string ctype: The name of the API to use.
:param string op: The API operation to perform.
:param JID jid: Optionally provide specific JID.
:param string node: Optionally provide specific node.'

def restore_default(self, ctype, op, jid=None, node=None):

    self.unregister(ctype, op, jid, node)
    self.register(self._handler_defaults[ctype][op], ctype, op, jid, node)
