Ukraine

...after the U.S. and Ukraine this week signed a 10-year security agreement that Russian officials, including Putin, denounced as “null and void.”

You can't declare something "null and void", invalid, in your legal system if it doesn't even exist in your legal system.

Like, you aren't a party to this. It's got nothing to do with you.

Unless the claim here is that it violates the US or the Ukrainian constitutions or something like that and they're talking about those systems, which I assume is not what's going on.

https://www.reuters.com/world/europe/ukraine-calls-russias-election-occupied-territories-null-void-2024-03-14/

Ukraine calls Russia's election in occupied territories null and void

See, that is meaningful. Ukraine's saying that they don't recognize the authority of the elected people as representing the people there; they aren't going to deal with them or extend them authority. Whether Ukraine recognizes the people there has some impact on its actions.

But Russia isn't going to deal with the agreement or extend it authority. There isn't any question of them recognizing it or not recognizing it.