title: Django 'SessionStore' object has no attribute '_session_cache'
body: <p>I am currently getting spammed by the error:</p>
  
  <p><code>dictionary update sequence element #0 has length 14; 2 is required</code> that seems to be provoked by <code>('SessionStore' object has no attribute '_session_cache')</code></p>
  
  <p>I read in this question: <a href="https://stackoverflow.com/questions/27180353/django-project-looking-for-attribute-session-cache">Django project looking for &quot;attribute &#39;_session_cache&#39;&quot;</a> that the issue might be that I don't have the <code>django_session</code> table, but I do and it's filled with content.</p>
  
  <p>Any idea what could provoke that?</p>
  
  <p>I am on Python <code>3.6.7</code>, django <code>2.1.7</code></p>
  
  <p>Here is the full error stack:</p>
  
  <pre><code>File "/path/to/venv/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in _get_session
    190.             return self._session_cache
  
  During handling of the above exception ('SessionStore' object has no attribute '_session_cache'), another exception occurred:
  
  File "/path/to/venv/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
    34.             response = get_response(request)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/utils/deprecation.py" in __call__
    90.             response = self.process_request(request)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/middleware/locale.py" in process_request
    21.         language = translation.get_language_from_request(request, check_path=i18n_patterns_used)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/utils/translation/__init__.py" in get_language_from_request
    222.     return _trans.get_language_from_request(request, check_path)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/utils/translation/trans_real.py" in get_language_from_request
    464.         lang_code = request.session.get(LANGUAGE_SESSION_KEY)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in get
    66.         return self._session.get(key, default)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in _get_session
    195.                 self._session_cache = self.load()
  
  File "/path/to/venv/lib/python3.6/site-packages/django/contrib/sessions/backends/db.py" in load
    43.         s = self._get_session_from_db()
  
  File "/path/to/venv/lib/python3.6/site-packages/django/contrib/sessions/backends/db.py" in _get_session_from_db
    34.                 expire_date__gt=timezone.now()
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/manager.py" in manager_method
    82.                 return getattr(self.get_queryset(), name)(*args, **kwargs)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/query.py" in get
    390.         clone = self.filter(*args, **kwargs)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/query.py" in filter
    844.         return self._filter_or_exclude(False, *args, **kwargs)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/query.py" in _filter_or_exclude
    862.             clone.query.add_q(Q(*args, **kwargs))
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/sql/query.py" in add_q
    1263.         clause, _ = self._add_q(q_object, self.used_aliases)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/sql/query.py" in _add_q
    1289.                 joinpromoter.add_votes(needed_inner)
  
  File "/path/to/venv/lib/python3.6/site-packages/django/db/models/sql/query.py" in add_votes
    2171.         self.votes.update(votes)
  
  File "/usr/lib/python3.6/collections/__init__.py" in update
    620.                     super(Counter, self).update(iterable) # fast path when counter is empty
  
  Exception Type: ValueError
  Exception Value: dictionary update sequence element #0 has length 14; 2 is required
  </code></pre>