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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 get_mbid(self):
 """Returns the MusicBrainz ID of the album or track."""


        doc = self._request(self.ws_prefix + ".getInfo", cacheable=True)

        try:
            lfm = doc.getElementsByTagName("lfm")[0]
            opus = next(self._get_children_by_tag_name(lfm, self.ws_prefix))
            mbid = next(self._get_children_by_tag_name(opus, "mbid"))
            return mbid.firstChild.nodeValue
        except StopIteration:
            return None