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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(raw):
 """Helper to construct a node from a dict. Args: raw (dict):
 Raw node representation. Returns: Node: A Node object or None. """

    ncls = None
    _type = raw.get('type')
    try:
        ncls = _type_map[NodeType(_type)]
    except (KeyError, ValueError) as e:
        logger.warning('Unknown node type: %s', _type)
        if DEBUG:
            raise_from(exception.ParseException('Parse error for %s' % (_type), raw), e)
        return None
    node = ncls()
    node.load(raw)

    return node