python 重构和JSON数据解析

看到一个重构的例子，还能重温json数据解析
# def GreetUser():
#     filename = '/Users/zhangxl/Desktop/union.json'
#     try:
#         with open(filename) as f_obj:
#             username = json.load(f_obj)
#     except FileNotFoundError:
#         username = input("What is your name？：")
#         with open(filename,'w') as f_obj:
#             json.dump(username,f_obj)
#             print(username)
#     else:
#         print("Welcome to " + username)

def get_stored_username():
    filename = '/Users/zhangxl/Desktop/union.json'
    try:
        with open(filename) as f_obj:
            username = json.load(f_obj)
    except FileNotFoundError:
        return None
    else:
        return username

def get_new_username():
    username = input("What is your name？：")
    filename = '/Users/zxl/Desktop/union.json'
    with open(filename,'w') as f_obj:
        json.dump(username,f_obj)
    return  username

def greet_user():
    username = get_stored_username()
    if username:
        print("Welcome  back ," + username )
    else:
        username = get_new_username()
        print("We will remember you when you come back" + username)

greet_user()

遇到问题：当文件内容为空是，会报错 。带运行一次后，我删除：union.json 文件内容，报错：raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)，所以我添加了一个ValueError