JakeWarthon stated here https://youtrack.jetbrains.com/issue/KT-20358 that this bug has been solved in Android Gradle 3.3 Alpha 11 plugin but I can reproduce it in Android Gradle 4.0 Alpha 6 plugin.

val map = mapOf<String, String>()
map.getOrDefault("foo", "bar")

This gives no warning from either the compiler or lint and crashes at runtime (on Lollipop) with

Fatal Exception: java.lang.NoSuchMethodError

Am I missing something?

Possibly it is a regression. I recommend creating a project that reproduces the problem, then filing a bug report with Google.