:param dict|None env_vars: Env vars to customize
    :param dict env: Original env vars

def added_env_paths(env_vars, env=None):
    """
    :param dict|None env_vars: Env vars to customize
    :param dict env: Original env vars
    """
    if not env_vars:
        return None

    if not env:
        env = dict(os.environ)

    result = dict(env)
    for env_var, paths in env_vars.items():
        separator = paths[0]
        paths = paths[1:]
        current = env.get(env_var, "")
        current = [x for x in current.split(separator) if x]

        added = 0
        for path in paths.split(separator):
            if path not in current:
                added += 1
                current.append(path)

        if added:
            result[env_var] = separator.join(current)

    return result