This error is mostly generated by outdated WordPress themes and/or plugins on sites which use WooCommerce.
After coming across it myself several times I finally found a good/simple fix on this page.
It says the offending code can be easily located by running the following command in your themes-folder:
grep -R -n "cart->get_cart_url"
Any occurrence of
WC()->cart->get_cart_url() needs to be replaced with