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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 update_payload(self, fields=None):
 """Convert ``sync_date`` to a string if datetime object provided."""

        data = super(SyncPlan, self).update_payload(fields)
        if isinstance(data.get('sync_date'), datetime):
            data['sync_date'] = data['sync_date'].strftime('%Y-%m-%d %H:%M:%S')
        return data