def to_list(obj):
    """Convert a list-like object to a list.

    >>> to_list([1, 2, 3])
    [1, 2, 3]

    >>> to_list("a,b,c")
    ['a', 'b', 'c']

    >>> to_list("item")
    ['item']

    >>> to_list(None)
    []

    """
    if isinstance(obj, (list, tuple)):
        return obj
    elif isinstance(obj, str):
        text = obj.strip()
        if ',' in text and ' ' not in text:
            return text.split(',')
        else:
            return text.split()
    elif obj is not None:
        return [obj]
    else:
        return []
