source map doesn't get created on CSS

[Gruski]

Source map file doesn't get created when minifying and bundling CSS even though it is configured to do so:

  {
    "outputFileName": "Bundles/bundle.css",
    "inputFiles": [
      "AppThemes/V2/*.css",
      "Vue/Components/*.css"
    ],
    "sourceMap": true
  }

Works with JS files.