addDefault adds underscore even if nameHint provided

Documentation shows an example without underscore
https://babeljs.io/docs/en/next/babel-helper-module-imports.html#import-hintedname-from-source

But in fact, it is added to the name
https://github.com/babel/babel/blob/e498bee10f0123bb208baa228ce6417542a2c3c4/packages/babel-helper-module-imports/test/index.js#L299

I understand why an underscore is necessary for _default(a reserved word). But I can't understand why it's necessary when nameHint is provided.

Should we change documentation or implementation?

Compare the documented example at the Babel helper module imports page with the behavior and assertion around packages/babel-helper-module-imports/test/index.js#L299. First determine whether the intended result is a documentation correction or an implementation change; the work is done when the chosen behavior and its documentation agree.

Written by the indexing model from the issue text.