code: public static <K, V> ImmutableSortedMap<K, V> copyOf(Map<? extends K, ? extends V> map) {
      // Hack around K not being a subtype of Comparable.
      // Unsafe, see ImmutableSortedSetFauxverideShim.
      @SuppressWarnings("unchecked")
      Ordering<K> naturalOrder = (Ordering<K>) NATURAL_ORDER;
      return copyOfInternal(map, naturalOrder);
    }
docs: Returns an immutable map containing the same entries as {@code map}, sorted by the natural
  ordering of the keys.
  
  <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.
  
  <p>This method is not type-safe, as it may be called on a map with keys that are not mutually
  comparable.
  
  @throws ClassCastException if the keys in {@code map} are not mutually comparable
  @throws NullPointerException if any key or value in {@code map} is null
  @throws IllegalArgumentException if any two keys are equal according to their natural ordering