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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_link(self, link_id=None, dump=True):
 """ Create a link. By default the link is empty :param dump: Dump topology to disk """

        if link_id and link_id in self._links:
            return self._links[link_id]
        link = UDPLink(self, link_id=link_id)
        self._links[link.id] = link
        if dump:
            self.dump()
        return link