def add_if_missing(add_this, path_list_str):
    """
    if a path is missing in a path list separated by ';',
    append it
    """
    path_list = path_list_str.split(';')

    if add_this in path_list:
        pass
    else:
        path_list.append(add_this)
    return ';'.join(path_list)