There are a lot of people here bashing dart. I for one really enjoy using it. I find it easy to understand and use. Unfortunately it is a bit pigeon-holed at the moment as the Flutter language. I'll admit the dart ecosystem does need more diversity, but the language itself seems to be attracting unwarranted disdain.
I don't know. Perhaps it is cool to hate on things you don't personally like? If dart is not for you I can understand that, but why does everyone want to rain on Dart's parade?

Go went? Go is still growing strong as far as I am aware.

You can still have nullable values in dart. They just have to be explicitly used.

int foo = null; // Trying to assign null to a variable of type integer will cause a compile time error.

int? nullableFoo = null; // This is A.O.K. as the variable is declared as a nullable integer.

This headline is not really news for anyone who is using Dart. It is a change that has been in the works for a long time, and null-safe dart (what we are talking about here.) has been standard for years now. Users of legacy code are able to disable null safety with a compiler flag. Come v3 that flag will be removed.