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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 from_json(cls, raw):
 """Helper to construct a blob from a dict. Args: raw (dict):
 Raw blob representation. Returns: NodeBlob: A NodeBlob object or None. """

        if raw is None:
            return None

        bcls = None
        _type = raw.get('type')
        try:
            bcls = cls._blob_type_map[BlobType(_type)]
        except (KeyError, ValueError) as e:
            logger.warning('Unknown blob type: %s', _type)
            if DEBUG:
                raise_from(exception.ParseException('Parse error for %s' % (_type), raw), e)
            return None
        blob = bcls()
        blob.load(raw)

        return blob