TypeError: 'NoneType' object is not callable

TypeError: 'NoneType' object is not callable

def login(func):
    def _login(*args, **kwargs):
        if account["is_authenticated"] is False:
            user = input('user:')
            password = input('password:')
            if user == account["username"] and password == account["password"]:
                print("welcome %s" % user)
                account["is_authenticated"] = True
            else:
                print("wrong username or password!")

        if account["is_authenticated"]:
                func(*args, **kwargs)

        return _login

@login
def sichuan():
    print("sichuan region.")

sichuan()

错误信息是：“NoneType” 对象不可调用，报错提示在最后一行，原因在于装饰器外部函数应该返回内部函数的地址，上面代码并没有返回，导致此错误发生。