Just tried out Dotty 0.2.0-RC1 today and I found it suprising that the following code compiles: def take(b: Boo | Null): Boo = { val z: Boo = b z } I can find some tidbits of discussion on https://gitter.im/lampepfl/dotty, but there doesn’t seem to be an issue on github tracking discussion on this topic. Everything being nullable has always been one of those “yeah but we don’t do that” moments in