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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 an annotation from a dict. Args: raw (dict):
 Raw annotation representation. Returns: Node: An Annotation object or None. """

        bcls = None
        if 'webLink' in raw:
            bcls = WebLink
        elif 'topicCategory' in raw:
            bcls = Category
        elif 'taskAssist' in raw:
            bcls = TaskAssist
        elif 'context' in raw:
            bcls = Context

        if bcls is None:
            logger.warning('Unknown annotation type: %s', raw.keys())
            return None
        annotation = bcls()
        annotation.load(raw)

        return annotation