.flatMap(unused -> ImmutableList.copyOf(elems).stream()));
  }

  public void testMapWithIndex_closeIsPropagated_sizedSource() {
    testMapWithIndex_closeIsPropagated(Stream.of("a", "b", "c"));
  }

  public void testMapWithIndex_closeIsPropagated_unsizedSource() {
    testMapWithIndex_closeIsPropagated(
        Stream.<@Nullable Object>of((Object) null).flatMap(unused -> Stream.of("a", "b", "c")));
  }