title: Python Flask - Login - UndefinedError: 'None' has no attribute 'is_authenticated'
body: <p>Am using Python , Flask-Login,</p>
  
  <p>The below line from a Flask html </p>
  
  <pre><code>{% if current_user.is_authenticated() %
  </code></pre>
  
  <p>throws below error in Ubuntu OS, and works fine in Windows OS(W7)</p>
  
  <pre><code> File "/home/user/workspace/test/templates/layout.html", line 27, in top-level template code
      {% if current_user.is_authenticated() %}
  UndefinedError: 'None' has no attribute 'is_authenticated'
  </code></pre>