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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 chunk_size(self, value):
 """Set the blob's default chunk size. :type value: int :param value: (Optional) The current blob's chunk size, if it is set. :raises: :class:`ValueError` if ``value`` is not ``None`` and is not a multiple of 256 KB. """

        if value is not None and value > 0 and value % self._CHUNK_SIZE_MULTIPLE != 0:
            raise ValueError(
                "Chunk size must be a multiple of %d." % (self._CHUNK_SIZE_MULTIPLE,)
            )
        self._chunk_size = value