webpack.config.module.ruleForStylesheets.js

      {
        test: /\.(css|pcss)/,
        use: [
          'style',
          {
            loader: 'css',
            options: {
              importLoaders: 1,
              sourceMap: isDebug,
              modules: true,
              localIdentName: isDebug ? '[name]_[local]_[hash:base64:3]' : '[hash:base64:4]',
              minimize: !isDebug,
            },
          },
          {
            loader: 'postcss',
            options: { // TypeError: Cannot read property 'config' of null ... at node_modules\postcss-load-config\index.js:50:22
              parser: 'sugarss',
              map: isDebug ? 'inline' : false,
              plugins: () => [
                require('postcss-smart-import'),
                require('postcss-easy-import')({ extensions: ['.pcss'] }),
                require('precss'),
                require('postcss-cssnext'),
                require('postcss-flexibility'),
                require('postcss-nested-props'),
              ],
            },
          },
        ],
      }