code: public static <K, V> ImmutableSortedMap<K, V> copyOf(
        Map<? extends K, ? extends V> map, Comparator<? super K> comparator) {
      return copyOfInternal(map, checkNotNull(comparator));
    }
docs: Returns an immutable map containing the same entries as {@code map}, with keys sorted by the
  provided comparator.
  
  <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
  @throws IllegalArgumentException if any two keys are equal according to the comparator