* static final ImmutableClassToInstanceMap<Handler> HANDLERS =
   *     new ImmutableClassToInstanceMap.Builder<Handler>()
   *         .put(FooHandler.class, new FooHandler())
   *         .put(BarHandler.class, new SubBarHandler())
   *         .put(Handler.class, new QuuxHandler())
   *         .build();
   * }
   *
   * <p>After invoking {@link #build()} it is still possible to add more entries and build again.