Fixed #26764 -- Fixed Session.cycle_key() crash on unaccessed session.

django/contrib/sessions/backends/base.py

@@ -306,7 +306,10 @@ class SessionBase(object):
         """
         Creates a new session key, while retaining the current session data.
         """
-        data = self._session_cache
+        try:
+            data = self._session_cache
+        except AttributeError:
+            data = {}
         key = self.session_key
         self.create()
         self._session_cache = data

tests/sessions_tests/tests.py

@@ -188,6 +188,10 @@ class SessionTestsMixin(object):
         self.assertNotEqual(self.session.session_key, prev_key)
         self.assertEqual(list(self.session.items()), prev_data)
 
+    def test_cycle_with_no_session_cache(self):
+        self.assertFalse(hasattr(self.session, '_session_cache'))
+        self.session.cycle_key()
+
     def test_save_doesnt_clear_data(self):
         self.session['a'] = 'b'
         self.session.save()