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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 block_uid(value: Union[str, BlockUID, None]) -> BlockUID: """ Convert value to BlockUID instance :param value: Value to convert :return: """

    if isinstance(value, BlockUID):
        return value
    elif isinstance(value, str):
        return BlockUID.from_str(value)
    elif value is None:
        return BlockUID.empty()
    else:
        raise TypeError("Cannot convert {0} to BlockUID".format(type(value)))