Of course I'm joking, but I think implicit nullability is the worst part of Go. A language designed in a era when this was widely known as the billion dollar mistake (prolly even more expensive).
But this is not easily reversed. Not as easy as tagging generics onto the language. And the parallels with Java's maturing are just lovely. Also, we have seen what Kotlin is now doing for Java: a new language was needed to truly fix that one mistake (implicit nullability), introduced in the grandparent of Java (namely C), and the great old grand uncle of Go.
But this is not easily reversed. Not as easy as tagging generics onto the language. And the parallels with Java's maturing are just lovely. Also, we have seen what Kotlin is now doing for Java: a new language was needed to truly fix that one mistake (implicit nullability), introduced in the grandparent of Java (namely C), and the great old grand uncle of Go.