In recent publication Brian Goetz explains why it is so complex to introduce one: https://mail.openjdk.org/pipermail/valhalla-spec-experts/2023-May/002276.html

In recent publication Brian Goetz explains why it is so complex to introduce one: https://mail.openjdk.org/pipermail/valhalla-spec-experts/2023-May/002276.html https://mail.openjdk.org/pipermail/valhalla-spec-experts/202... Great read. TLDR: It is hard to decide what the defaults should looks like, so they plan to add special markers (! and ?) to allow programmers to pass that detail to objects with "undefined nullability" (without ! or ?).