Like Spring Data did, it would be nice for both Java and Kotlin developers to leverage in Spring Boot 2 null-safety annotations (@Nullable etc) in most common Spring Boot APIs like SpringApplication and TestRestTemplate.

These annotations are now flexible enough to just target the API of these 2 classes if we want (annotating all Spring Boot would be nice but we probably don't have the time for that).

I can contribute such feature via a PR, I would mainly need guidance on what are the most common APIs used in addition to the 2 proposed.