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.

This causes certain operations to misbehave. For example, in JShell:

new TreeSet<Integer>().subSet(-1, 1).spliterator().tryAdvance(null);    // returns false
new TreeSet<Integer>().subSet(-1, 1).spliterator().forEachRemaining(null);    // does nothing
new TreeSet<Integer>().subSet(-1, 1).stream().forEach(null);    // does nothing

However, the specifications for Spliterator's tryAdvance() and forEachRemaining() methods require throwing a NullPointerException if the argument is null. In addition, the Stream class has a general requirement that behavioral parameters (such as the parameter to forEach) must be non-null, implying that NullPointerException is thrown in such cases.

Solution

Add explicit null checks in the corresponding methods of these spliterator implementations.

Specification

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