if (value == null) {
        tryDrainReferenceQueues();
        return null;
      }

      return value;
    }

    /**
     * Performs routine cleanup following a read. Normally cleanup happens during writes, or from
     * the cleanupExecutor. If cleanup is not observed after a sufficient number of reads, try
     * cleaning up from the read thread.
     */
    void postReadCleanup() {

 *
 * @param <K> the most general key type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@code
 *     #removalListener}. Cache keys may not be null.
 * @param <V> the most general value type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@code