The problem with optionals - as Sonar will complain about - is that people will call `.get()` on an Optional without first checking `.isPresent()` for example.
Lots of things in the language that allow you to shoot yourself in the foot that other languages have solved.
Also, isn't there a static code analysis tool that checks at compile-time that reference variables annotated as @non_nullable can never be null?
assert foo != null : "foo must not be null - remember to wrap optional data in Optional<T>"
If asserts are disabled, then the null pointer checks are still inserted by the JVM.
Think about it like this: in Java - all class references were Option<Class> by default - and what was truly lacking was the possibility of having a non-optional reference[1]. They could've treated transparently all old-code[2] references as Option<ClassName>, and just given you the possibility of having non-optional reference in the new code (that meant that you can't pass objects with non-optional references to the legacy libraries, but it's a pain that could've gone away pretty quickly as libraries got recompiled to the new java versions)
[1] Oracle's interpretation was the other way around: "Java lacks the Option type, let's add it". I argue they got it wrong - Java always had the Option type, it's just that it was implicit; and since Java was lacking the non-optional types, you couldn't do anything useful with the Option, other than check for "None" (i.e. null).
[2] By "old code" I mean "old compiled code". You keep the binary compatibility - but indeed, you would need to drop the source-level compatibility, since compiling old code with the new compiler would not have worked. But, again, that would be fixable with a "legacy syntax" compiler flag, that would produce old-style binaries from old-style source code.
In terms of backwards compatibility the language teams position, IIRC, was that in the cases where you are intentionally using null it's quite easy to find and flag flag the nullable variable, but in all other cases the unexpected nullability can responsibly be removed from apps, making then-unnecessary null checks superfluous.
It's a bold move, but if it works at scale Java might be able to pull the tablecloth out from under the plates too...
It's still entirely possible to get a nil from Objective-C while the API is declared as nonnullable, this even happened to me with Apple's own API's if abused to a certain limit.
It is a way to introduce the benefits (as long as the library is developed properly) of non-nullable types without sacrificing retro compatibility.
Edit: I remember a bug in earlier version of Swift Cocoa binding where getting calendar events without titles would hang without possibility of recourse because of this problems.