这个有关于函数返回值的问题，不知道如何改正，请改正一下！

def unlock(content):
    content = content.split("|")
    string = []
    for i in content:
        if i == '渋':
            i = 'C'
            string.append(i)
        elif i == '哋':
            i = "D"
            string.append(i)
        elif i == '榆':
            i = "U"
            string.append(i)
        elif i == '戼':
            i = ":"
            string.append(i)
        elif i == '筻':
            i = "\\"
            string.append(i)
        elif i == '槇':
            i = "."
            string.append(i)
        else:
            pass
        if i == '誒':
            i = "a"
            string.append(i)
        elif i == '荸':
            i = "b"
            string.append(i)
        elif i == '罒':
            i = "c"
            string.append(i)
        elif i == '籴':
            i = "d"
            string.append(i)
        elif i == '懿':
            i = "e"
            string.append(i)
        elif i == '諨':
            i = "f"
            string.append(i)
        elif i == '嵇':
            i = "g"
            string.append(i)
        elif i == '篪':
            i = "h"
            string.append(i)
        elif i == '嗳':
            i = "i"
            string.append(i)
        elif i == '尐':
            i = "j"
            string.append(i)
        elif i == '尅':
            i = "k"
            string.append(i)
        elif i == '歐':
            i = "l"
            string.append(i)
        elif i == '尛':
            i = "m"
            string.append(i)
        elif i == '峎':
            i = "n"
            string.append(i)
        elif i == '鏂':
            i = "o"
            string.append(i)
        elif i == '疋':
            i = "p"
            string.append(i)
        elif i == '窟':
            i = "q"
            string.append(i)
        elif i == '嬭':
            i = "r"
            string.append(i)
        elif i == '噝':
            i = "s"
            string.append(i)
        elif i == '悐':
            i = "t"
            string.append(i)
        elif i == '肀':
            i = "u"
            string.append(i)
        elif i == '徫':
            i = "v"
            string.append(i)
        elif i == '':
            i = "w"
            string.append(i)
        elif i == '薖':
            i = "x"
            string.append(i)
        elif i == '韤':
            i = "y"
            string.append(i)
        elif i == '榟':
            i = "z"
            string.append(i)
        else:
            pass
    if type(string) == list:
        return string
    else:
        return 'wrong'

这段代码在使用返回值时报错：

Traceback (most recent call last):
File "C:\Users\惠普\Desktop\music- player\music.py", line 204, in <module>
  main()
File "C:\Users\惠普\Desktop\music- player\music.py", line 58, in main
  f, name = get_filelist(path)  # 遍历文件夹
TypeError: cannot unpack non-iterable NoneType object

函数get_filelist函数是这样的：

ef get_filelist(path):
    """
    定义函数：用于遍历文件
    """
    Filelist = []
    name_list_gobal = []
    for home, dirs, files in os.walk(path):
        for filename in files:
            # 文件名列表，包含完整路径
            Filelist.append(os.path.join(home, filename))
            # 文件名列表，只包含文件名
            name_list_gobal.append(filename)
        return Filelist, name_list_gobal