Class 'WC_Session' not found in class-wc-session-handler.php
<p>I have plugin <code>"Woocommerce Email Cart"</code> and it was running fine on <code>Woocommerce 2.2</code>. When I upgrade that to <code>Woocommerce 2.5.2</code> I got this few errors including this. I fixed the other issues but I'm unable to fix this.
I got error saying:-</p>

<blockquote>
  <p>Fatal error: Class 'WC_Session' not found in
  /home/31776xa/public_html/wp-content/plugins/woocommerce/includes/class-wc-session-handler.php
  on line 18</p>
</blockquote>

<pre><code>$woocommerce-&gt;frontend_includes();
$session_class = apply_filters( 'woocommerce_session_handler', 'WC_Session_Handler' );
$woocommerce-&gt;session  = new $session_class();
$woocommerce-&gt;cart     = new WC_Cart();  
$woocommerce-&gt;customer = new WC_Customer();
</code></pre>