如题，用的$luogu3$主题，设置背景图片$URL$后点保存显示“操作成功”却无用，$F12$的$console$中有如下错误信息：

themeConfig.js?ver=20171214:1
Uncaught TypeError: Cannot set properties of undefined (setting 'background_image')
    at a (themeConfig.js?ver=20171214:1:18691)
    at u.setBindValue (themeConfig.js?ver=20171214:6:37517)
    at u.e [as setBindValue] (themeConfig.js?ver=20171214:1:166050)
    at u.set [as bindValue] (themeConfig.js?ver=20171214:6:37427)
    at input (themeConfig.js?ver=20171214:6:38914)
    at n (themeConfig.js?ver=20171214:1:172383)
    at HTMLInputElement.t._withTask.t._withTask (themeConfig.js?ver=20171214:1:171791)