> But, most importantly, the fundamental issue is that all classes are optional by default in Java (indeed, that's the problem at hand). Adding an Optional class doesn't really mean you can make any non-nullability assumptions about other classes, especially when using different libraries.

Perhaps it's just me, but I don't equate optional with nullable. An optional value is just the designer specifying that you may or many not specify that value, while nullable are objects which may or may not have been initialized yet.

Even though nullables have been used and abused to represent optional values, I'm not sure it's a good idea to conflate both. It would be like in C++ equating shared pointers with optional types.