Entry<K, V> prevEntry = entryItr.next();
    while (entryItr.hasNext()) {
      Entry<K, V> nextEntry = entryItr.next();
      assertTrue(comparator.compare(prevEntry.getKey(), nextEntry.getKey()) < 0);
      prevEntry = nextEntry;
    }
  }

   * (pointing to the nextEntry entry in the linked list). The pointers in [size(), entries.length)
   * are all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "nextEntry" pointer equal to {@code ENDPOINT} is the last node.
   */
  @VisibleForTesting transient long[] links;