The treaties created with nations that have no king or queen are harmless - and have no true value except for a line on a national diplomacy list.
A single king or queen who takes over the nation can easily nullify the treaty with laws or let it be; peace treaties only have teeth if there are hostility laws, so if a nation wishes to collect treaties at this time, let them do it!
When additional diplomatic features and functions arrive, those treaties may bear much more of a burden than they currently bear, or not.
Besides, while it may be a simple line of code to remedy, there are many other tweaks and features the devs are working on that are worth more to PG.
I say let them collect them - there be more pressing business worth our efforts.