fix: add defaultExport in empty export

[houhongxu]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

if i have an empty less file
with config like this

 {
      test: /\.module\.less$/,
      use: [
        prodEnv
          ? {
              loader: MiniCssExtractPlugin.loader,
              options: {
                defaultExport: true,
              },
            }
          : require.resolve("style-loader"),
        {
          loader: require.resolve("css-loader"),
          options: {
            esModule: true,
            modules: {
              namedExport: true,
            },
          },
        },
        require.resolve("less-loader"),
      ],
}

i got an error

ModuleDependencyError: export 'default' (imported as 'styles') was not found in './index.module.less' (possible exports: container)

in mini-css-extract-plugin/loader.js function makeResult, when locals===undefined esModule===true defaultExport===true, only return export {}

this pr add the export {}; export default {}

Breaking Changes

Additional Info

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: alexander-akait / name: Alexander Akait (1703161)
• ✅ login: houhongxu / name: HHX (69a46dd)

[alexander-akait]

Can you add a test case?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.39%. Comparing base (c7ff30d) to head (1703161).
Report is 15 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1108      +/-   ##
==========================================
- Coverage   90.61%   85.39%   -5.22%     
==========================================
  Files           5        5              
  Lines         895     1041     +146     
  Branches      255      305      +50     
==========================================
+ Hits          811      889      +78     
- Misses         74      128      +54     
- Partials       10       24      +14     

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[alexander-akait]

Thank you

[houhongxu]

Thank you

Thank you 😝