[interestingemu]

I have seen plenty of libraries using null to indicate an error. If this wasn't the case, as you allege, then why do Kotlin devs act like it's such a big deal? Why add a language feature for something that isn't even considered an issue instead of e.g. improving how Kotlin handles checked exceptions?

[lmm]

One thing I find really frustrating is that Ceylon didn't take advantage of its union types to represent checked exceptions that way :(