Optional<? extends Number> first = numbers.first();
    // Number value = first.or(0.5); // error
  }

  @SuppressWarnings("unused") // compilation test
  public void testSampleCodeFine1() {
    Optional<Number> optionalInt = Optional.of((Number) 1);
    Number value = optionalInt.or(0.5); // fine
  }

  @SuppressWarnings("unused") // compilation test
  public void testSampleCodeFine2() {