ImmutableListMultimap.of("a", "1", "@", "2", "b", "3");
    assertThrows(IllegalArgumentException.class, () -> mediaType.withParameters(parameters));
  }

  public void testWithParameters_nonAsciiParameter() {
    MediaType mediaType = MediaType.parse("text/plain");
    ImmutableListMultimap<String, String> parameters = ImmutableListMultimap.of("…", "a");