@Override
    public void fill(Supplier<E> s, WaitStrategy wait, ExitCondition exit) {
        MessagePassingQueueUtil.fill(this, s, wait, exit);
    }
{@inheritDoc}
<p>
Because return null indicates queue is empty we cannot simply rely on next element visibility for poll
and must test producer index when next element is not visible.
jctools-core/src/main/java/org/jctools/queues/atomic/unpadded/MpmcAtomicUnpaddedArrayQueue.java