fold throws NPE when using parallel() variant on the collection

[Arul Dhesiaseelan]

Hi,

This code used to work before, but it fails with build 61 and with the
latest sources. It works fine with stream, but not in parallel in the fold
context.

    List<String> greetings = Arrays.asList("hello", "Hello");
    List<Tweet> tweets = new ArrayList<>();
    tweets.add(new Tweet("arul", "Aloha!", 2));
    tweets.add(new Tweet("joe", "Hello!", 16));
    tweets.add(new Tweet("matt", "Hola!", 78));

    List<Tweet> filtered = tweets.parallel().filter(t ->
greetings.parallel().anyMatch(t.text::contains)).into(new
ArrayList<Tweet>());//greetings.parallel() works
    List<Tweet> filtered2 = tweets.parallel().filter(tweet ->
greetings.parallel().fold(() -> false, (Boolean b, String keyword) -> b ||
tweet.text.contains(keyword), null)).into(new ArrayList<Tweet>());//
greetings.parallel() fails with NPE when used with fold()

Exception in thread "main" java.lang.NullPointerException
    at java.util.streams.ops.FoldOp$ReduceTask.onCompletion(FoldOp.java:123)
    at
java.util.concurrent.CountedCompleter.tryComplete(CountedCompleter.java:389)
    at java.util.streams.ops.AbstractTask.compute(AbstractTask.java:101)
    at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:435)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:263)
    at
java.util.concurrent.ForkJoinPool$WorkQueue.runSubtask(ForkJoinPool.java:994)
    at
java.util.concurrent.ForkJoinPool.tryHelpStealer(ForkJoinPool.java:1704)
    at java.util.concurrent.ForkJoinPool.awaitJoin(ForkJoinPool.java:1833)
    at java.util.concurrent.ForkJoinTask.doJoin(ForkJoinTask.java:345)
    at java.util.concurrent.ForkJoinTask.join(ForkJoinTask.java:657)
    at java.util.concurrent.ForkJoinPool.invoke(ForkJoinPool.java:2196)
    at
java.util.streams.AbstractPipeline$ParallelImplPipelineHelper.invoke(AbstractPipeline.java:263)
    at java.util.streams.ops.FoldOp.evaluateParallel(FoldOp.java:86)
    at
java.util.streams.AbstractPipeline.evaluateParallel(AbstractPipeline.java:125)
    at
java.util.streams.AbstractPipeline.evaluateParallel(AbstractPipeline.java:113)
    at java.util.streams.AbstractPipeline.evaluate(AbstractPipeline.java:87)
    at
java.util.streams.AbstractPipeline.pipeline(AbstractPipeline.java:298)
    at java.util.streams.ValuePipeline.fold(ValuePipeline.java:189)
    at FilterTest$2.test(FilterTest.java:25)
    at FilterTest$2.test(FilterTest.java:1)
    at java.util.streams.ops.FilterOp$1.accept(FilterOp.java:62)
    at java.util.streams.Streams$ArraySpliterator.into(Streams.java:711)
    at
java.util.streams.ParallelPipelineHelper.into(ParallelPipelineHelper.java:57)
    at
java.util.streams.AbstractPipeline$ParallelImplPipelineHelper.into(AbstractPipeline.java)
    at
java.util.streams.ops.TreeUtils$CollectorTask.doLeaf(TreeUtils.java:120)
    at
java.util.streams.ops.TreeUtils$CollectorTask.doLeaf(TreeUtils.java:98)
    at java.util.streams.ops.AbstractTask.compute(AbstractTask.java:100)
    at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:435)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:263)
    at
java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:975)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1479)
    at
java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:104)

-Arul