def unpack(dic):
    """
    Unpack lists with only one member

    Parameters
    ----------
    dic : dict
        A nested dictionary

    Returns
    -------
    dict
        A dictionary that its value unlisted
    """
    if dic == None:
        return None
    dix = dict()
    for x, y in dic.items():
        if isinstance(y, list) and len(y) == 1:
            dix[x] = y[0]
        elif y == []:
            dix[x] = None
        else:
            dix[x] = y
    return dix