Unexpected token at nullish coalescing

[dnbeats]

The exact error is the following

client?ecf9:159 ./src/js/options.js 205:13
Module parse failed: Unexpected token (205:13)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
| const a = undefined;
| const b = 9999;

alert(a ?? b);

| })
| // ! EXPORT E IMPORT

I think that is the acorn module which must be actualized in order to include the nullish coalescing but I am working on it, I am very new to this. If there is anyone who dealed with that, please, share the solution.