Method subSet

guava/src/com/google/common/collect/Maps.java:3957–3960

(@ParametricNullness K fromElement, @ParametricNullness K toElement)

    }

    @Override
    public SortedSet<K> subSet(@ParametricNullness K fromElement, @ParametricNullness K toElement) {
      return new SortedKeySet<>(map().subMap(fromElement, toElement));
    }

    @Override
    public SortedSet<K> headSet(@ParametricNullness K toElement) {