Where can I find the php file including $empty ?

[ed0522]

I'm reading PS code, but I can't find the php file handling with $empty.

 

Where is the file? Can someone help me?

 

{if isset($empty)}

<p class="alert alert-warning">{l s='Your shopping cart is empty.'}</p>

{elseif $PS_CATALOG_MODE}

<p class="alert alert-warning">{l s='This store has not accepted your new order.'}</p>

{else}