}

    @Override
    public @Nullable K higherKey(K key) {
      return standardHigherKey(key);
    }

    @Override
    public @Nullable Entry<K, V> firstEntry() {
      return standardFirstEntry();
    }

    /*
     * We can't override lastEntry to delegate to standardLastEntry, as it would create an infinite
     * loop. Instead, we test standardLastEntry manually below.
     */