*
   * {@snippet :
   * import static com.google.common.collect.ImmutableMap.toImmutableMap;
   * ...
   * ImmutableMap<Color, String> colorNames =
   *     allColors.stream().collect(toImmutableMap(c -> c, c -> c.toString()));
   * }
   *
   * <p>Streams provide a more standard and flexible API and the lambdas make it clear what the keys