postcss-import Reproduction

Repository created using the following commands:

ng new postcss-test
npm install @clr/ui --save

? Do you want to enforce stricter type checking and stricter bundle budgets in the workspace?
  This setting helps improve maintainability and catch bugs ahead of time.
  For more information, see https://angular.io/strict No
? Would you like to add Angular routing? No
? Which stylesheet format would you like to use? CSS

styles.css populated with:

/* This line causes the error */
@import "../node_modules/@clr/ui/clr-ui-dark.min.css" screen and (prefers-color-scheme: dark);

/* This import succeeds without problem */
/*@import "../node_modules/@clr/ui/clr-ui-dark.min.css";*/

Reproduce

npm install
npm run ng build
√ Browser application bundle generation complete.

Error: ./src/styles.css
Module build failed (from ./node_modules/mini-css-extract-plugin/dist/loader.js):
ModuleBuildError: Module build failed (from ./node_modules/postcss-loader/dist/cjs.js):
TypeError: Cannot read property '0' of undefined
    at C:\Users\James\Projects\postcss-test\node_modules\postcss-import\index.js:78:37
    at Array.forEach (<anonymous>)
    at applyMedia (C:\Users\James\Projects\postcss-test\node_modules\postcss-import\index.js:70:16)
    at C:\Users\James\Projects\postcss-test\node_modules\postcss-import\index.js:51:9
    at async LazyResult.runAsync (C:\Users\James\Projects\postcss-test\node_modules\postcss\lib\lazy-result.js:358:11)
    at async Object.loader (C:\Users\James\Projects\postcss-test\node_modules\postcss-loader\dist\index.js:95:14)
    at C:\Users\James\Projects\postcss-test\node_modules\webpack\lib\NormalModule.js:316:20
    at C:\Users\James\Projects\postcss-test\node_modules\loader-runner\lib\LoaderRunner.js:367:11
    at C:\Users\James\Projects\postcss-test\node_modules\loader-runner\lib\LoaderRunner.js:233:18
    at context.callback (C:\Users\James\Projects\postcss-test\node_modules\loader-runner\lib\LoaderRunner.js:111:13)
    at Object.loader (C:\Users\James\Projects\postcss-test\node_modules\postcss-loader\dist\index.js:104:7)
 @ multi ./src/styles.css styles[0]

Error: ./src/styles.css (./node_modules/css-loader/dist/cjs.js??ref--13-1!./node_modules/postcss-loader/dist/cjs.js??ref--13-2!./src/styles.css)
Module build failed (from ./node_modules/postcss-loader/dist/cjs.js):
TypeError: Cannot read property '0' of undefined
    at C:\Users\James\Projects\postcss-test\node_modules\postcss-import\index.js:78:37
    at Array.forEach (<anonymous>)
    at applyMedia (C:\Users\James\Projects\postcss-test\node_modules\postcss-import\index.js:70:16)
    at C:\Users\James\Projects\postcss-test\node_modules\postcss-import\index.js:51:9
    at async LazyResult.runAsync (C:\Users\James\Projects\postcss-test\node_modules\postcss\lib\lazy-result.js:358:11)
    at async Object.loader (C:\Users\James\Projects\postcss-test\node_modules\postcss-loader\dist\index.js:95:14)