Category "kotlin-null-safety"

How is Dart "sound null-safety" different from Kotlin null safety?

This Dart official video states that Dart's so-called "sound null safety" is better than Kotlin's null safety design, because it can optimise the code based on

kotlin inverse boolean safe casting

Let's say I have an object Response. Now I would like to check a boolean variable, success, under Response and do an early return is response is not successful.