requests.cookies.RequestsCookieJar: popitem() does not work

requests.cookies.RequestsCookieJar's popitem() method doesn't seem to work even if cookies is not empty.

Expected Result

From the doc:

remove and return some (key, value) pair as a 2-tuple; but raise KeyError if D is empty.

(Also, I'm not sure what exactly is "D" here. I assume it means the cookies obj itself.)

Actual Result

It always raises KeyError even when it's not empty.

Reproduction Steps

import requests

r = requests.get('https://google.com')
print(len(r.cookies)) # = 3

r.cookies.popitem()

System Information

$ python -m requests.help

{
  "chardet": {
    "version": "4.0.0"
  },
  "charset_normalizer": {
    "version": "2.0.10"
  },
  "cryptography": {
    "version": "3.4.8"
  },
  "idna": {
    "version": "2.10"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.9.1"
  },
  "platform": {
    "release": "10",
    "system": "Windows"
  },
  "pyOpenSSL": {
    "openssl_version": "101010cf",
    "version": "20.0.1"
  },
  "requests": {
    "version": "2.28.1"
  },
  "system_ssl": {
    "version": "1010107f"
  },
  "urllib3": {
    "version": "1.26.3"
  },
  "using_charset_normalizer": false,
  "using_pyopenssl": true
}

Start by reproducing the issue with the provided requests.get and r.cookies.popitem() snippet, then inspect RequestsCookieJar.popitem and its surrounding cookie-container behavior. Done means popitem() removes and returns a (key, value) pair from a non-empty jar while still raising KeyError for an empty jar.