### Describe the bug

https://github.com/developer-choi/axios-error-report

TypeError is occurred (in 1.6.6 version)

<img width="184" alt="image" src="https://github.com/axios/axios/assets/51902362/1f7f6e7f-8c8b-4ef7-9854-5c08f572d58b">

<img width="171" alt="image" src="https://github.com/axios/axios/assets/51902362/36042439-a071-485e-b696-9f2c01849759">

### To Reproduce

https://github.com/developer-choi/axios-error-report

### Code snippet

_No response_

### Expected behavior

_No response_

### Axios Version

1.6.6

### Adapter Version

_No response_

### Browser

CHROME

### Browser Version

120.0.6099.225

### Node.js Version

20.11.0

### OS

Window 11
test/unit/adapters/http.js
done();
      }).catch(done);
    });
  });
  it('should support basic auth with a header', function (done) {
    server = http.createServer(function (req, res) {
      res.end(req.headers.authorization);
    }).listen(4444, function () {
      var auth = { username: 'foo', password: 'bar' };
      var headers = { AuThOrIzAtIoN: 'Bearer 1234' }; /
      axios.get('http://localhost:4444/', { auth: auth, headers: headers }).then(function (res) {
        var base64 = Buffer.from('foo:bar', 'utf8').toString('base64');
        assert.equal(res.data, 'Basic ' + base64);
        done();
      }).catch(done);
    });
  });
  it('should provides a default User-Agent header', function (done) {
    server = http.createServer(function (req, res) {
      res.end(req.headers['user-agent']);
    }).listen(4444, function () {
      axios.get('http://localhost:4444/').then(function (res) {
        assert.ok(/^axios\/[\d.]+[-]?[a-z]*[.]?[\d]+$/.test(res.data), `User-Agent header does not match: ${res.data}`);
        done();
      }).catch(done);
    });
  });
  it('should allow the User-Agent header to be overridden', function (done) {
    server = http.createServer(function (req, res) {
      res.end(req.headers['user-agent']);