Hi,
That error is a second, separate spot in the FedEx 2 plugin: it read the state/province code from the address without checking that a state was actually set. When the address has no state (which is normal while the address is still being typed, or for countries that have no states), reading the state raised the "zone_code_3 on null" warning, and on United States and Puerto Rico addresses the plugin then sent an empty state to FedEx, which FedEx rejects, so no rate came back.
We have fixed it: the plugin now reads the state safely and only sends a state to FedEx when one is actually present, so an address with just a country and a postcode should still gets rates if FedEx allows for it.
Download again the install package of HikaShop on our website and install it on yours and you'll have the new patch.
One thing to keep in mind: the live shipping refresh asks FedEx for rates as you type, so the FedEx method only appears once the address is complete enough for FedEx to quote (at least the country and the postcode). If it still does not appear once the address is filled in with the patched file, please turn on the FedEx plugin's debug option, reproduce the issue, and look at the bottom of the "Payment log file" in the HikaShop configuration. It should provide information on what's going on.