code: public void addConverter(ValueConverter<?, ?> converter) {
  
      getInitializationState().requireNotInitilized();
      if (this.converters == null) {
        this.converters = new ArrayList<>();
      }
      this.converters.add(converter);
    }
docs: This method registers the given {@code converter} to this composed converter.
  
  @param converter is the converter to add.