code: private static <K, V> ImmutableSortedMap<K, V> of(Comparator<? super K> comparator, K k1, V v1) {
      return new RegularImmutableSortedMap<K, V>(
          new RegularImmutableSortedSet<K>(ImmutableList.of(k1), checkNotNull(comparator)),
          ImmutableList.of(v1));
    }
docs: Returns an immutable map containing a single entry.