"Destination web/js/jquery.min.js not written because src files were empty." with structure-asset-processing-with-grunt.md

[user1007017]

Hi
If I follow the guide, first I'm getting some errors because of grunt dependencies,
but over all 'grunt build' returns

Destination web/js/jquery.min.js not written because src files were empty.

The browser debugging console shows some missing file lib.min.js which I can't find anywhere.
http://yii2-basic.mydomain.com/js/lib.min.js?v=

What might be the problem?

[Alexander Makarov]

Source file for jquery is empty.