title: PHP session false not set
body: <p>When setting false value to session, the session is set, but the value is empty. The type is boolean.
  This code:</p>
  
  <pre><code>&lt;?php
      session_start();
      $_SESSION["IsMobile1"] = false;
      $_SESSION["IsMobile2"] = true;
      //header("location: ../../../index.php");
      echo "IsSet1: " . isset($_SESSION["IsMobile1"]) . "; IsMobile1: " . $_SESSION["IsMobile1"] . "; type: " . gettype($_SESSION["IsMobile1"]) . ";&lt;br&gt;";
      echo "IsSet2: " . isset($_SESSION["IsMobile2"]) . "; IsMobile2: " . $_SESSION["IsMobile2"] . ";&lt;br&gt;";
  ?&gt;
  </code></pre>
  
  <p>prints out:</p>
  
  <pre><code>IsSet1: 1; IsMobile1: ; type: boolean;
  IsSet2: 1; IsMobile2: 1;
  </code></pre>
  
  <p>My PHP version is 5.5.13.
  Is this expected behaviour? I am trying to read the session with code:</p>
  
  <pre><code>if (isset($_SESSION["IsMobile"]))
      {
          if (is_bool($_SESSION["IsMobile"]))
          {
              header("location: Mobile/");
              exit;
          }
      }
  </code></pre>
  
  <p>but of course it is not working, because IsMobile is empty boolean. (In original I just use IsMobile. IsMobile1 and IsMobile2 is just for testing).</p>