code: @SuppressWarnings("unchecked")
    public static <K, V> ImmutableSortedMap<K, V> copyOfSorted(SortedMap<K, ? extends V> map) {
      Comparator<? super K> comparator = map.comparator();
      if (comparator == null) {
        // If map has a null comparator, the keys should have a natural ordering,
        // even though K doesn't explicitly implement Comparable.
        comparator = (Comparator<? super K>) NATURAL_ORDER;
      }
      if (map instanceof ImmutableSortedMap) {
        // TODO(kevinb): Prove that this cast is safe, even though
        // Collections.unmodifiableSortedMap requires the same key type.
        @SuppressWarnings("unchecked")
        ImmutableSortedMap<K, V> kvMap = (ImmutableSortedMap<K, V>) map;
        if (!kvMap.isPartialView()) {
          return kvMap;
        }
      }
      return fromEntries(comparator, true, map.entrySet());
    }
docs: Returns an immutable map containing the same entries as the provided sorted map, with the same
  ordering.
  
  <p>Despite the method name, this method attempts to avoid actually copying the data when it is
  safe to do so. The exact circumstances under which a copy will or will not be performed are
  undocumented and subject to change.
  
  @throws NullPointerException if any key or value in {@code map} is null