code: public boolean add(String inputKey, String inputValue) {
          String key = Normalizer.normalize(inputKey, Normalizer.NORMALIZE_LOWER);
          String value = Normalizer.normalize(inputValue, Normalizer.NORMALIZE_LOWER);
          if (!contains(this.values.get(key), value)) {
              addElement(key, value);
              return true;
          }
          return false;
      }
docs: Add the given key=value pair to this handler.
  
  @param inputKey
  @param inputValue
  @return boolean (true means success adding)