### 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
res.send(JSON.stringify(req.body));
      });
      server = app.listen(3001, function () {
        return axios.post('http://localhost:3001/', obj, {
          headers: {
            'content-type': 'application/x-www-form-urlencoded'
          }
        })
          .then(function (res) {
            assert.deepStrictEqual(res.data, obj);
            done();
          }).catch(done);
      });
    });
  });
  it('should respect formSerializer config', function (done) {
    const obj = {
      arr1: ['1', '2', '3'],
      arr2: ['1', ['2'], '3'],
    };
    const form = new URLSearchParams();
    form.append('arr1[0]', '1');
    form.append('arr1[1]', '2');
    form.append('arr1[2]', '3');
    form.append('arr2[0]', '1');
    form.append('arr2[1][0]', '2');
    form.append('arr2[2]', '3');
    server = http.createServer(function (req, res) {
      req.pipe(res);
    }).listen(3001, () => {