I'd argue that they are fundamentally different. Option is "just another type". You interact with it using constructors, map/flatMap/get etc. You could implement Optional in Java 1.5 but can't implement nullable types in current Java.

Nullable types are a feature of the type system and require language support, but the benefit is that you don't touch typical programming patterns

   val foo: T? = x()
   if(foo == null) { return ... }
   // foo is now T, optionality gone

v.s.

   val foo: Option<T> = x()
   // following must be wrapped and sprinkled in .map, .flatMap, .orElse

You can sort-of achieve the first with .isPresent() + .get(), but it clutters the scope, is more verbose, and is not really idiomatic.