How to handle nulls when using Java collection sort

Question

When using Collection.sort in Java what should I return when one of the inner objects is null

Example:

Collections.sort(list, new Comparator

        

Answer 1

if comparing two property, attr1 natural order, attr2 reverse order, and attr2 can be null:

datas.sort(comparing(Data::getAttr1, naturalOrder()).
        thenComparing(Data::getAttr2, nullsLast(reverseOrder())));