Fixed #26520 -- Fixed a regression where SessionBase.pop() didn't return a KeyError.

    TEST_COOKIE_NAME = 'testcookie'

    TEST_COOKIE_VALUE = 'worked'

    __not_given = object()

    def __init__(self, session_key=None):

        self._session_key = session_key

        self.accessed = False

    def get(self, key, default=None):

        return self._session.get(key, default)

    def pop(self, key, default=None):

    def pop(self, key, default=__not_given):

        self.modified = self.modified or key in self._session

        return self._session.pop(key, default)

        args = () if default is self.__not_given else (default,)

        return self._session.pop(key, *args)

    def setdefault(self, key, value):

        if key in self._session:

* Prevented ``makemigrations`` from generating infinite migrations for a model

  field that references a ``functools.partial`` (:ticket:`26475`).

* Fixed a regression where ``SessionBase.pop()`` returned ``None`` rather than

  raising a ``KeyError`` for nonexistent values (:ticket:`26520`).

      Example: ``fav_color = request.session.get('fav_color', 'red')``

    .. method:: pop(key, default=None)

    .. method:: pop(key, default=__not_given)

      Example: ``fav_color = request.session.pop('fav_color', 'blue')``

        self.assertTrue(self.session.accessed)

        self.assertFalse(self.session.modified)

    def test_pop_no_default_keyerror_raised(self):

        with self.assertRaises(KeyError):

            self.session.pop('some key')

    def test_setdefault(self):

        self.assertEqual(self.session.setdefault('foo', 'bar'), 'bar')

        self.assertEqual(self.session.setdefault('foo', 'baz'), 'bar')