[krzysdz]

This PR is based on #1560, with the following changes:

• req._unset is initialised to {} in both Node.js and browser versions (should prevent this._unset is undefined in the browser #1573),
• there are no changes related to Content-Type, because it is possible to unset it¹.

Warning

The new tests run only on Node.js, because only the Node.js code sets the default Accept-Encoding. The tests do not prevent a regression like #1573, because .unset() tests can be found only in test/node/.

Closes #1860

Checklist

• I have ensured my pull request is not behind the main or master branch of the original repository.
• I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
• I have written a commit message that passes commitlint linting.
• I have ensured that my code changes pass linting tests.
  None of the lint warnings are from my code.
• I have ensured that my code changes pass unit tests.
• I have described my pull request and the reasons for code changes along with context if necessary.

Footnotes

1. Except that request.post('/sth').send({ name: 'tj' }).unset('Content-Type').end() will fail, because the data cannot be serialised as serialisation function is chosen in ._end() based on the Content-Type. This probably should be another issue. ↩

[titanism]

Thanks for this, and for the original report in #1860. #1865 and #1867 took the same approach, and the combined commit credits this PR as the first. Compared with it, the commit creates the unset record only when unset() is called, keeps the header unset after redirects, and removes headers regardless of capitalization. Closing in favor of that commit, released in v10.4.2 and now available on npm: https://github.com/forwardemail/superagent/releases/tag/v10.4.2

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