以下为小程序后台出现的错误内容，请问如何解决？ Cannot read property 'avatar' of undefined TypeError: Cannot read property 'avatar' of undefined at success (https://miniprogram:///pages/index/index.js:208:55) at Function.i.<computed> (https://lib/WASubContext.js:2:1837671) at https://lib/WASubContext.js:2:112384 at d (https://lib/WASubContext.js:2:467131) at Function.<anonymous> (https://lib/WASubContext.js:2:629975) at https://lib/WASubContext.js:2:112384 at https://lib/WASubContext.js:2:604669