docs: private String joinEnumNames(String separator) {
      E[] enumTypes = enumClass.getEnumConstants();
      StringBuilder sb = new StringBuilder();
      for(int i = 0; i < enumTypes.length; ++i) {
        if(i > 0) {
          sb.append(separator);
        }
        sb.append(enumTypes[i].name());
      }
      return sb.toString();
    }