I could point out how it's way, way easier in java programs, since we're picking on java, to skip over doing things like this. Or I could point out how the bar to do things correctly is lower in this hcl example than the equivalent java. Or I could point out how the things I named as best practices can look in the real world, which seems to be the best course of discussion since unfamiliarity seems to be an issue here:

You have a type defined, it's just string. There's no default, which means it's a required input. Required inputs obviously can't have a default. Arbitrary strings are a perfectly acceptable input and without seeing how that variable is actually used, I can't speculate about validation criteria and it is very reasonable that for arbitrary strings there are none.