def coalesce(*xs):
    """
    Coalescing monoid operation: return the first non-null argument or None.

    Examples:
        >>> coalesce(None, None, "not null")
        'not null'
    """
    if len(xs) == 1:
        xs = xs[0]
    for x in xs:
        if x is not None:
            return x
    return None