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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 argument_kind(args):
 # type: (List[Argument]) -> Optional[str] """Return the kind of an argument, based on one or more descriptions of the argument. Return None if every item does not have the same kind. """

    kinds = set(arg.kind for arg in args)
    if len(kinds) != 1:
        return None
    return kinds.pop()