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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 missing_revisions(self, doc_id, *revisions):
 """ Returns a list of document revision values that do not exist in the current remote database for the specified document id and specified list of revision values. :param str doc_id: Document id to check for missing revisions against. :param list revisions: List of document revisions values to check against. :returns: List of missing document revision values """

        url = '/'.join((self.database_url, '_missing_revs'))
        data = {doc_id: list(revisions)}

        resp = self.r_session.post(
            url,
            headers={'Content-Type': 'application/json'},
            data=json.dumps(data, cls=self.client.encoder)
        )
        resp.raise_for_status()

        resp_json = response_to_json_dict(resp)
        missing_revs = resp_json['missing_revs'].get(doc_id)
        if missing_revs is None:
            missing_revs = []

        return missing_revs