ListMultimap<String, Integer> unmod = Multimaps.unmodifiableListMultimap(mod);
    assertNotSame(mod, unmod);
    assertSame(unmod, Multimaps.unmodifiableListMultimap(unmod));
    ImmutableListMultimap<String, Integer> immutable =
        ImmutableListMultimap.of("a", 1, "b", 2, "a", 3);
    assertSame(immutable, Multimaps.unmodifiableListMultimap(immutable));
    assertSame(

   */
  public static <K extends @Nullable Object, V extends @Nullable Object>
      ListMultimap<K, V> unmodifiableListMultimap(ListMultimap<K, V> delegate) {
    if (delegate instanceof UnmodifiableListMultimap || delegate instanceof ImmutableListMultimap) {
      return delegate;
    }
    return new UnmodifiableListMultimap<>(delegate);
  }

  /**
   * Simply returns its argument.
   *