@Override
    @ParametricNullness
    public K firstKey() {
      return sortedMap().firstKey();
    }

    @Override
    @ParametricNullness
    public K lastKey() {
      return sortedMap().lastKey();
    }

    @Override
    public SortedMap<K, Collection<V>> headMap(@ParametricNullness K toKey) {
      return new SortedAsMap(sortedMap().headMap(toKey));
    }

      return standardFirstKey();
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return standardHeadMap(toKey);
    }

    @Override
    public K lastKey() {
      return standardLastKey();
    }

    @Override
    public SortedMap<K, V> tailMap(K fromKey) {
      return standardTailMap(fromKey);
    }
  }

      return transformEntries(fromMap().headMap(toKey), transformer);
    }

    @Override
    @ParametricNullness
    public K lastKey() {
      return fromMap().lastKey();
    }

    @Override
    public SortedMap<K, V2> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {

            the filesystem if explicitly provided, then in the reactor if groupId and artifactId are provided,
            then in the default parent directory, then the local repository, and lastly in the remote repo.
            However, if the both relative path and the group ID / artifact ID are provided,
            they must match the file in the location given.