docs: @Nullable
    public CloseableReference<CloseableImage> getForReuse() {
      while (true) {
        CacheKey key = popFirstFreeItemKey();
        if (key == null)  {
          return null;
        }
        CloseableReference<CloseableImage> imageRef = mBackingCache.reuse(key);
        if (imageRef != null) {
          return imageRef;
        }
      }
    }