[2270] How does the 'generate' work with middleware ?

I found a problem what is, I want to use a middleware which called 'userAgent'

in nuxt.config.js,like this: router: { middleware: 'userAgent', }, as the document said.

but, when I run 'npm run generate' code, it warning

{ Error: ENOENT: no such file or directory, lstat '/Users/summerd/Documents/ workspace/cy/ssr-template/dist/index.html' errno: -2, code: 'ENOENT', syscall: 'lstat', path: '/Users/summerd/Documents/workspace/cy/ssr-template/dist/index.html' }

and the dist fold I can't find index.html and 200.html. Does any body know something about this, and know how can I build successfully with router: { middleware: 'xxxx' } ?