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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 _dump(cls, obj, *, context, **kwargs):
 """ obj -> dict """

        if obj is None:
            return None
        dump = context["engine"]._dump
        filtered = filter(
            lambda item: item[1] is not None,
            ((
                column.dynamo_name,
                dump(column.typedef, getattr(obj, column.name, None), context=context, **kwargs)
            ) for column in cls.Meta.columns))
        return dict(filtered) or None