fix path argument must be of type string error

[patrick99e99]

This PR contains a:

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

Motivation / Use-Case

Intermittently the call to this.outputs.get(file); is undefined. Checking for the presence of this file and waiting if its not there fixes the problem.

10 12 2020 18:37:17.496:ERROR [karma-server]: UnhandledRejection
infrastructure_error TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined
    at validateString (internal/validators.js:125:11)
    at Object.join (path.js:1147:7)
    at Plugin.<anonymous> (/Users/me/my-app/node_modules/karma-webpack/dist/karma-webpack.js:318:70)
    at Plugin.readFile (/Users/me/my-app/node_modules/karma-webpack/dist/karma-webpack.js:334:5)
    at /Users/me/my-app/node_modules/karma-webpack/dist/karma-webpack.js:353:19
    at executeProcessor (/Users/me/my-app/node_modules/karma/lib/preprocessor.js:28:11)
    at runProcessors (/Users/me/my-app/node_modules/karma/lib/preprocessor.js:41:23)
    at /Users/me/my-app/node_modules/karma/lib/preprocessor.js:144:9
    at module.exports (/Users/me/my-app/node_modules/isbinaryfile/index.js:29:12)
    at readFileCallback (/Users/me/my-app/node_modules/karma/lib/preprocessor.js:116:7)
    at /Users/me/my-app/node_modules/graceful-fs/graceful-fs.js:90:16
    at FSReqWrap.readFileAfterClose [as oncomplete] (internal/fs/read_file_context.js:53:3)
From previous event:
    at Promise.map (/Users/me/my-app/node_modules/karma/lib/file-list.js:89:51)
From previous event:
    at Promise.map (/Users/me/my-app/node_modules/karma/lib/file-list.js:89:25)
    at runCallback (timers.js:705:18)
    at tryOnImmediate (timers.js:676:5)
    at processImmediate (timers.js:658:5)
From previous event:
    at FileList._refresh (/Users/me/my-app/node_modules/karma/lib/file-list.js:64:8)
    at FileList.refresh (/Users/me/my-app/node_modules/karma/lib/file-list.js:158:29)
    at Server.refreshFiles (/Users/me/my-app/node_modules/karma/lib/server.js:146:44)
    at Plugin.notifyKarmaAboutChanges (/Users/me/my-app/node_modules/karma-webpack/dist/karma-webpack.js:250:16)
    at Plugin.done (/Users/me/my-app/node_modules/karma-webpack/dist/karma-webpack.js:193:12)
    at AsyncSeriesHook.eval [as callAsync] (eval at create (/Users/me/my-app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:27:1)
    at AsyncSeriesHook.lazyCompileHook (/Users/me/my-app/node_modules/tapable/lib/Hook.js:154:20)
    at Watching._done (/Users/me/my-app/node_modules/webpack/lib/Watching.js:98:28)
    at compiler.emitRecords.err (/Users/me/my-app/node_modules/webpack/lib/Watching.js:73:19)
    at Compiler.emitRecords (/Users/me/my-app/node_modules/webpack/lib/Compiler.js:499:39)
    at compiler.emitAssets.err (/Users/me/my-app/node_modules/webpack/lib/Watching.js:54:20)
    at hooks.afterEmit.callAsync.err (/Users/me/my-app/node_modules/webpack/lib/Compiler.js:485:14)
    at _promise0.then._result0 (eval at create (/Users/me/my-app/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:13:1)

Breaking Changes

Additional Info

[thijstriemstra]

@patrick99e99 can you make this pull request against the next branch?

[codymikol]

Is this still something you're interested in?

[codymikol]

The cases where this happens should be handled in v5, thanks for your contribution though!