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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_dbxref(self, feature_id, db, accession, organism=None, sequence=None):
 """ Add a dbxref to a feature :type feature_id: str :param feature_id: Feature UUID :type db: str :param db: DB Name (e.g. PMID) :type accession: str :param accession: Accession Value :type organism: str :param organism: Organism Common Name :type sequence: str :param sequence: Sequence Name This seems to show two attributes being added, but it behaves like those two are one. :rtype: dict """

        data = {
            'features': [
                {
                    'uniquename': feature_id,
                    'dbxrefs': [
                        {
                            'db': db,
                            'accession': accession,
                        }
                    ]
                }
            ]
        }
        data = self._update_data(data, organism, sequence)
        return self.post('addDbxref', data)