docs: public PeriodConverter getPeriodConverter(Object object) {
          PeriodConverter converter =
              (PeriodConverter)iPeriodConverters.select(object == null ? null : object.getClass());
          if (converter != null) {
              return converter;
          }
          throw new IllegalArgumentException("No period converter found for type: " +
              (object == null ? "null" : object.getClass().getName()));
      }