code: public static void register() {
          try {
              Class<? extends List<Object>> listObjectClass;
              listObjectClass = (Class<List<Object>>) NumberedListConverter.class
                                  .getMethod("getString", List.class).getParameterTypes()[0];
              NumberedListConverter converter = new NumberedListConverter();
              ConverterRegistry.addConverter(listObjectClass, converter);
              ConverterRegistry.addConverter(ArrayList.class, new NumberedArrayListConverter(converter));
          } catch (RuntimeException e) {
              throw e;
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      }
docs: Makes NumberedListConverter the Converter Slim will uses for (Array)Lists.