Gulp gives error when concat-css, minifyCSS?

Question

gulp.js

Gulp gives error when concat-css, minifyCSS?

I don't understand why this is happening? Separately, the file is concatenated. Swears at the following:

events.js:72
        throw er; // Unhandled 'error' event
              ^
TypeError: Cannot use 'in' operator to search for 'keepSpecialComments' in bundle.min.css
    at CleanCSS.minify (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\clean-css\lib\clean.js:88:30)
    at CleanCSS.minify (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\clean-css\lib\clean.js:75:19)
    at minify (C:\WebDev\Education\node_modules\gulp-minify-css\index.js:25:33)
    at DestroyableTransform.modifyContents [as _transform] (C:\WebDev\Education\node_modules\gulp-minify-css\index.js:79:25)
    at DestroyableTransform.Transform._read (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:184:10)
    at DestroyableTransform.Transform._write (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\through2\node_modules\readable-stream\lib\_stream_transform.js:172:12)
    at doWrite (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\through2\node_modules\readable-stream\lib\_stream_writable.js:237:10)
    at writeOrBuffer (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\through2\node_modules\readable-stream\lib\_stream_writable.js:227:5)
    at DestroyableTransform.Writable.write (C:\WebDev\Education\node_modules\gulp-minify-css\node_modules\through2\node_modules\readable-stream\lib\_stream_writable.js:194:11)
    at DestroyableTransform.ondata (C:\WebDev\Education\node_modules\gulp-concat-css\node_modules\through2\node_modules\readable-stream\lib\_stream_readable.js:572:20)

Answer 1

Check the files for the presence of comments of this kind, inside the class.
Try to "take out" all comments from {} and put them higher or lower.