doTestEmpty(noneOf("CharMatcher"));
    doTestEmpty(inRange('n', 'q'));
    doTestEmpty(forPredicate(Predicates.equalTo('c')));
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  public void testNull() throws Exception {
    doTestNull(CharMatcher.any());
    doTestNull(CharMatcher.none());
    doTestNull(is('a'));
    doTestNull(isNot('a'));
    doTestNull(anyOf(""));
    doTestNull(anyOf("x"));