### 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
});
  it('should supply a user-agent if one is not specified', function (done) {
    server = http.createServer(function (req, res) {
      assert.equal(req.headers["user-agent"], 'axios/' + axios.VERSION);
      res.end();
    }).listen(4444, function () {
      axios.get('http://localhost:4444/'
      ).then(function (res) {
        done();
      }).catch(done);
    });
  });
  it('should omit a user-agent if one is explicitly disclaimed', function (done) {
    server = http.createServer(function (req, res) {
      assert.equal("user-agent" in req.headers, false);
      assert.equal("User-Agent" in req.headers, false);
      res.end();
    }).listen(4444, function () {
      axios.get('http://localhost:4444/', {
        headers: {
          "User-Agent": null
        }
      }).then(function (res) {
        done();
      }).catch(done);
    });
  });
  it('should throw an error if http server that aborts a chunked request', function (done) {
    server = http.createServer(function (req, res) {
      res.writeHead(200, { 'Content-Type': 'text/plain' });