lessc : source-map with auto-prefix plugin make an error

[ppierre]

When using less-plugin-autoprefix with the --source-map option ; the CSS file is generated but lessc exit with an error :
(Rq: changing --source-map to --source-map-map-inline avoid the error)

cmd.exe /D /C call C:\......\node_modules\.bin\lessc.cmd --source-map --autoprefix test.less test.css
internal/fs/utils.js:793
  throw new ERR_INVALID_ARG_TYPE(
  ^

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received an instance of SourceMapGenerator
    at writeFile (fs.js:1487:5)
    at go$writeFile (C:\......\node_modules\graceful-fs\graceful-fs.js:138:14)
    at Object.writeFile (C:\......\node_modules\graceful-fs\graceful-fs.js:135:12)
    at writeSourceMap (C:\......\node_modules\less\bin\lessc:183:10)
    at writeSourceMapIfNeeded (C:\......\node_modules\less\bin\lessc:207:7)
    at C:\......\node_modules\less\bin\lessc:299:11
    at C:\......\node_modules\less\bin\lessc:237:11
    at C:\......\node_modules\graceful-fs\graceful-fs.js:143:16
    at C:\......\node_modules\graceful-fs\graceful-fs.js:61:14
    at FSReqCallback.oncomplete (fs.js:180:23) {
  code: 'ERR_INVALID_ARG_TYPE'
}

Process finished with exit code 1

Command executed by a "file watcher" of JetBrain IDE (PHPStrom). All parameters by default except adding --autoprefix
lessc installed locally as "devDependencies".

[ppierre]

My bad fixed by : #41
Why this pull request ins't apply ?