Fatal error when enable cart module

When i enable cart module, it works on eshop component page.
In other pages, for example: article page, i get error:
( ! ) Fatal error: Call to a member function getCosts() on a non-object in eshop\modules\mod_eshop_cart\mod_eshop_cart.php on line 65

I tried to edit this file:
modules/mod_eshop_cart/mod_eshop_cart.php
Line 63, add this:
require_once JPATH_SITE .'/components/com_eshop/models/cart.php';

And it works.

So let's check on this.