事情是介个样子的：
我给项目新配置了新的 redis 接口，再运行项目后，一直报错，说不能设置只有 getter 的属性名：

server error TypeError: Cannot set property name of  which has only a getter
    at defaultErrorHanlder (/Users/name/code/node_modules/koa-generic-session/lib/session.js:558:12)
    at /Users/name/code/node_modules/koa-generic-session/lib/session.js:98:13
    at Generator.throw (<anonymous>)
    at step (/Users/name/code/node_modules/koa-generic-session/lib/session.js:3:191)
    at /Users/name/code/node_modules/koa-generic-session/lib/session.js:3:402
    at processTicksAndRejections (internal/process/task_queues.js:97:5) {
  request: {
    method: 'GET',
    url: '/favicon.ico',
    header: {
      host: 'localhost:3000',
      connection: 'keep-alive',
      'user-agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.122 Safari/537.36',
      'sec-fetch-dest': 'image',
      accept: 'image/webp,image/apng,image/*,*/*;q=0.8',
      'sec-fetch-site': 'same-origin',
      'sec-fetch-mode': 'no-cors',
      referer: 'http://localhost:3000/',
      'accept-encoding': 'gzip, deflate, br',
      'accept-language': 'zh-CN,zh;q=0.9',
      cookie: 'koa.sid=OdvWGWA1RUH_IXywo3Cyc_jz3j9kr7iJ; koa.sid.sig=rLchHBrwX0adJ6O93FBTkbDaBwY'
    }
  },
  response: {
    status: 404,
    message: 'Not Found',
    header: [Object: null prototype] {}
  },
  app: { subdomainOffset: 2, proxy: false, env: 'development' },
  originalUrl: '/favicon.ico',
  req: '<original node req>',
  res: '<original node res>',
  socket: '<original node socket>'
}

解决：重新启动 redis。

$ redis-server restart