Cecil gives a full discussion of “exceptio probat regulam,” and (in response to Hugh) he mentions Cicero, in which he is absolutely correct. The man he was defending was from modern-day Cadiz in Spain, and there was an argument about the citizenship he’d been granted as a reward for his time in the military.
But pardon me for being an irritated Latinist. The man in question was Lucius Cornelius Balbus, not Bilbo–of course he has no relation to Frodo. I will give Cecil that the speech is the Pro Balbo, but even then there is no i; it is simply ablative.