My biggest pet peeve with Kotlin is that they got rid of checked exceptions and replaced them with nothing at all. All error code flow is now just invisible unchecked exceptions, the single worst kind of error handling imaginable.

I know they added the Result type later on, but there's zero convenience to it, so you have to manually handle every error, even if you just want to bubble it.

Checked Exceptions were better, though Rust still has the best error handling in any non-functional language.