Npm run hot fails with copy ()

Sample mix config:

This works with npm run hot

mix.js('resources/assets/js/app.js', 'public/js/app.js')
   .sass('resources/assets/sass/app.scss', 'public/css/app.css')

This doesn’t work with npm run hot and fails with unspecified error

mix.js('resources/assets/js/app.js', 'public/js/app.js')
   .sass('resources/assets/sass/app.scss', 'public/css/app.css')
   .copy ('resources/tmp', 'public/tmp'); 

 ERROR  Failed to compile with 1 errors

 error

[JeffreyWay]

Fixed in 329ed0ccffb51d52111ec11359f2617c528c60c0.

[TiBianMod]

Temporary solution disable mix.copy when you running npm run hot

if (! mix.config.options.hmr) {
    mix.copy('path/from', 'path/to');
}