Asset processing with Grunt  lib.js not exits

>`all.json` lists JavaScript files to process into `lib.js`.

But after run the `grunt build` 

```shell
Running "uglify:lib" (uglify) task
>> Destination web/js/lib.min.js not written because src files were empty.
>> No files created.
```

`web/js/lib.js`  not exits

I'm not sure if I'm mistaken, or `web/js/lib.js`  missing in the `Gruntfile.js` 😟 


