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# This work is licensed under the GNU GPLv2 or later.
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# See the COPYING file in the top-level directory.
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def listify(val):
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    """Ensure that value is either None or a list, converting single values
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    into 1-element lists"""
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    if val is None:
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        return val
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    if isinstance(val, list):
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        return val
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    return [val]