TypeError: Super expression must either be null or a function, not undefined

I am getting this error after upgrading to webpack v4. Strangely this happens only in the prod build and not in dev build.

This is the stack-trace in browser console:

TypeError: Super expression must either be null or a function, not undefined
bundle-f82b2570e6fa0145fdb8.js:22:54086
n.withStyles/</n</<
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:22:54086
n.withStyles/</n<
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:22:54066
n.withStyles/<
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:22:53698
<anonymous>
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:36:433740
t
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:1:105
<anonymous>
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:84:260717
t
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:1:105
<anonymous>
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:84:263006
t
http://localhost:8000/js/bundle-f82b2570e6fa0145fdb8.js:1:105

I am actually using react-dates which is using this library. From stacktrace, I suspect this is where the error is coming from. Also removing react-dates makes the error to go away.

Here is my entire webpack config: https://gist.github.com/tejasbubane/9ae4d2e099bef97b3b118f99a163294e

Relevant libraries and their versions:

"react": "^15.6.1",
"react-dates": "^15.5.3",
"react-with-styles": "=2.2.0",
"webpack": "^4.12.0",
"babel-core": "^6.26.3",
"babel-loader": "^7.1.4",
"babel-polyfill": "^6.26.0",

[sunstorymvp]

For anyone who run into this issue setting keep_fnames: true for uglifyjs helps. Maybe because of this https://github.com/mishoo/UglifyJS2/issues/3015#issuecomment-375185061

[lencioni]

Hard to say what might be happening here without more information.

According to this Stack Overflow post, it looks like this might happen if something extends React.component instead of React.Component. Do you think anything like that could be happening?

Could you post some of the code from your stack trace?