assertNull(outer.converterTo(inner).convert(null));
        assertNull(outer.converterTo(inner).reverse().convert(null));
      }
    }
  }

  public void testConverter_toString() {
    assertEquals(
        "LOWER_HYPHEN.converterTo(UPPER_CAMEL)", LOWER_HYPHEN.converterTo(UPPER_CAMEL).toString());
  }

  public void testConverter_serialization() {