title: Why is getSessionFromRedirect() return a NULL?
body: <p>I have the following code which redirects the user to log into facebook and tries to retrieve the session but the session is NULL:</p>
  
  <pre><code>&lt;?php
  
  session_start();
  
  require 'vendor/autoload.php';
  
  use Facebook\FacebookSession;
  use Facebook\FacebookRedirectLoginHelper;
  
  FacebookSession::setDefaultApplication('Foo', 'Bar');
  
  $helper = new FacebookRedirectLoginHelper('Baz');
  $loginUrl = $helper-&gt;getLoginUrl();  
  
  echo '&lt;a href="' . $loginUrl . '"&gt;Log In&lt;/a&gt;';  
  
  $session = $helper-&gt;getSessionFromRedirect();  
  
  // This displays [NULL] always
  echo '[' . gettype($session) . ']';
  
  ?&gt;
  </code></pre>
  
  <p>I don't understand why the $session is always NULL. Please help.</p>