Summary

For the subSet from a java.util.TreeSet or a java.util.TreeMap::keySet, if such a set is empty, its spliterator now properly throws NullPointerException for tryAdvance and forEachRemaining.

Problem

The subSet for a TreeSet or a TreeMap.entrySet() got a customized spliterator implementation in JDK-8011426. That patch incorrectly omitted null checks when the subSet is empty, because the arguments are unused for empty subSets.

For example, in JShell:

new TreeSet<Integer>().subSet(-1, 1).spliterator().tryAdvance(null)

returns false instead of throwing a NullPointerException.

Solution

Throw a NullPointerException instead of returning false for tryAdvance or return successfully for forEachRemaining for the spliterator of such empty subsets.

Specification

No change. This is a behavioral change that aligns implementation to specification.