@Override
        public void reduce(final NullObject key, final Iterator<Integer> values, final ReduceEmitter<NullObject, Integer> emitter) {
            int count = 0;
            while (values.hasNext()) {
                count = count + values.next();
            }
            emitter.emit(count);
        }
Javadoc for {@code ConcurrentSkipListSet} includes this little note: "Beware that, unlike in most
collections, the size method is not a constant-time operation." Doing a traversal of elements will yield
the correct count. Java 11 upgrade seemed to force this failure consistently.
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/computer/GraphComputerTest.java