Is there null in scoreboard? [closed]

You're probably thinking about Minecraft commands as a real programming language, but it isn't. It started from simple commands like teleportation, setting blocks, etc. and evolved into something that can be used for quite a lot, but it was never developed for that. If you think about it like a regular programming language, you'll encounter many cases like this, where something doesn't work quite as expected.

null doesn't even exist in all programming languages and in those where it exist, it can take many different forms, like null, Null, NULL, undefined, nil, undef, Nothing, etc. You can't expect it to work with the first spelling that comes to mind.

The closest you can get to null in Minecraft is a person that is not listed on a scoreboard. If it's an entity in the world (like a player, sheep or XP orb), you can target all that aren't in a scoreboard like this:

/execute as @e unless entity @s[scores={foo=..0}] unless entity @s[scores={foo=0..}] run <command>

You could also do it with one unless, but for that you would have to know the minimum and maximum value of a scoreboard and I also don't know that.