return fromMap().floorKey(key);
    }

    @Override
    public NavigableMap<K, V2> headMap(@ParametricNullness K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public NavigableMap<K, V2> headMap(@ParametricNullness K toKey, boolean inclusive) {
      return transformEntries(fromMap().headMap(toKey, inclusive), transformer);
    }

    @Override
    @CheckForNull