title: filter_input for session variables
body: <p>Is there some equivalent of <code>filter_input</code> I can use with <code>$_SESSION</code>as I would with <code>$_POST</code>?</p>
  
  <p>When I tried it gives the error :</p>
  
  <p><code>Warning: filter_input(): INPUT_SESSION is not yet implemented</code></p>
  
  <pre><code>session_start();
  $x=filter_input(INPUT_SESSION, 'x');
  if ($x){
      echo $x;
  }
  </code></pre>
  
  <p>php version: <code>PHP Version 5.5.12-1+deb.sury.org~precise+1</code></p>