Warning about mixing default and named exports with commonjs plugin

• Rollup Version: 1.31.0
• Operating System (or Browser): Ubuntu 18.04.3 LTS
• Node Version: 13.7.0

How Do We Reproduce?

Open this repo and run the bootstrap commands specified in README.md

Please also take a look at original-project-commonjs.output.js. I don't know what this invocation means there

export default commonjsHelpers.unwrapExports(main);

In my minimum reproduction commonjs.output.js file there is no unwrapExports(), however the warning is still left

Expected Behavior

No warnings

Actual Behavior

I get the following warning:

~/my/junk/rollup (master) $ npx rollup -c

./main.js → ./main.bundle.js...
(!) Mixing named and default exports
https://rollupjs.org/guide/en/#output-exports
The following entry modules are using named and default exports together:
main.js

Consumers of your bundle will have to use chunk['default'] to access their default export, which may not be what you want. Use `output.exports: 'named'` to disable this warning
created ./main.bundle.js in 30ms
~/my/junk/rollup (master) $ 

Start with the linked reproduction repository and follow the bootstrap commands in README.md, then run the Rollup command described in the issue. Compare original-project-commonjs.output.js with commonjs.output.js and inspect main.js to trace the mixed export warning. Done means the reproduction behavior is understood and the reported warning is corrected or clearly characterized.