Cannot build with Parcel: Unterminated regular expression

$ PRODUCT_TYPE=webapp parcel entry/src/index.html --open
Server running at http://localhost:1234 
⚠️  Could not load existing sourcemap of "../../node_modules/react-spreadsheet-grid/lib/bundle.js".
🚨  /node_modules/react-spreadsheet-grid/lib/bundle.js:520:83: Unterminated regular expression (520:83)
  518 |         if (sourceMap) {
  519 |                 // http://stackoverflow.com/a/26603875
> 520 |                 css += "\n + btoa(unescape(encodeURIComponent(JSON.stringify(sourceMap)))) + " */";
      |                                                                                                 ^
  521 |         }
  522 | 
  523 |         var blob = new Blob([css], { type: "text/css" });

• react-spreadsheet-grid version: 1.4.3
• parcel-bundler version: 1.12.4