@Nullable
  private synchronized CloseableReference<V> referenceToClose(Entry<K, V> entry) {
    Preconditions.checkNotNull(entry);
    return (entry.isOrphan && entry.clientCount == 0) ? entry.valueRef : null;
  }
Returns the value reference of the entry if it should be closed, null otherwise.
imagepipeline-base/src/main/java/com/facebook/imagepipeline/cache/LruCountingMemoryCache.java