The Nullless example uses null, implicitly (Nitpicking for fun)

[dylan-chong]

The field:

final Constrain<? super T> constrain;

is set to null implicitly since it is not set to anything, and the method:

Constrain<? super T> getConstrain() {
    return constrain;
  }

returns null... so perhaps it shouldn't be called 'Nullless'. It also means 'Nullless' exploits the same bug in the same way as 'Unsound.java in Java 8'.

Just saying! :P