@SuppressWarnings("unchecked")
        @Nullable
        public Reference<K, V> pollForPurge() {
            return (Reference<K, V>) this.queue.poll();
        }
Return any reference that has been garbage collected and can be purged from the
underlying structure or {@code null} if no references need purging. This
method must be thread safe and ideally should not block when returning
{@code null}. References should be returned once and only once.

@return a reference to purge or {@code null}
analyzer/src/main/java/nl/basjes/parse/useragent/utils/springframework/util/ConcurrentReferenceHashMap.java