public Optional<Integer> getPort() {
        if (0 == args.length) {
            return Optional.empty();
        }
        try {
            int port = Integer.parseInt(args[0]);
            if (port < 0) {
                return Optional.empty();
            }
            return Optional.of(port);
        } catch (final NumberFormatException ignored) {
            throw new IllegalArgumentException(String.format("Invalid port `%s`.", args[0]));
        }
    }
@Test
    void assertGetPortWithEmptyArgument() {
        assertFalse(new BootstrapArguments(new String[]{}).getPort().isPresent());
    }