Is headerModules working fine for you? weird concat.build overriding

[brunomacf]

I'm using this config in a addon i'm working on

cssModules: {
  headerModules: [
    'addon/styles/mystyle.scss',
  ],
  extension: 'scss',
  intermediateOutputPath: 'app/styles/_modules.scss',
}

Where i have a sass variable declared addon/styles/mystyle.scss' used by other components in the addon. I tracked the issue down and it seems the problem is in this line:

https://github.com/salsify/ember-css-modules/blob/master/packages/ember-css-modules/lib/output-styles-preprocessor.js#L64

We are overriding concat.build and when it gets called fixedHeaders is empty for some reason... although i'm seeing correct fixedHeaders if i log it outside concat.build.

Edit: I'm using ember-cli 3.17.3.

[lolmaus]

Please mention concat.build overriding in issue title, since without concat.build it's working fine for you and me.