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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 set_add(self, key, value, create=False, **kwargs):
 """ Add an item to a set if the item does not yet exist. :param key: The document ID :param value: Value to add :param create: Create the set if it does not exist :param kwargs: Arguments to :meth:`mutate_in` :return: A :class:`~.OperationResult` if the item was added, :raise: :cb_exc:`NotFoundError` if the document does not exist and `create` was not specified. .. seealso:: :meth:`map_add` """

        op = SD.array_addunique('', value)
        try:
            sdres = self.mutate_in(key, op, **kwargs)
            return self._wrap_dsop(sdres)
        except E.SubdocPathExistsError:
            pass