This gist of that is uncovered connectors are unsupported and void the warranty. Third party antennas are possible, but again unsupported and damage caused by them is not covered. The recommended option is a N Type dust cap, find an example below.
If it was me, I would still use a 50ohm load on an unused port (antenna or termination). A dust cap will present an open circuit to the port and if the port is ever enabled, 100% of the power gets reflected back into the radio... never a great thing for a radio.