NullPointerTester tester = new NullPointerTester();
    tester.testAllPublicInstanceMethods(converter);
  }

  public void testStringConverter_nullConversions() {
    Converter<String, TestEnum> converter = Enums.stringConverter(TestEnum.class);
    assertThat(converter.convert(null)).isNull();
    assertThat(converter.reverse().convert(null)).isNull();
  }