alt Hacker News...and Java didn't even have basic enums or sum types from the beginning. But it had null.
They added enums, they added sealed classes. They're trying to get rid of null (apparently it's really hard). The problem is that in 2012, when go 1.0 was released, this should have been obvious to everyone.
Here's a famous discussion from 2009, three years before the 1.0 release (tldr: facepalm)
I remember back in 1995 thinking that it was stupid for Java not to have generics, so instead you had to always cast Vector/Hashtable elements from Object, or implement your own type-specific container classes for every element type (and there wasn’t even a preprocessor to facilitate the latter).
Sum types I didn’t really miss, because you can implement a type-safe equivalent using the Visitor pattern, and retain an interface-implementation separation that native sum types typically don’t provide.