docs: private final void addAttributeShort(String key, String value) {
          this._toString = null; // reset toString variable
          ArrayList<String> array = this._attributes.get(key);
          if (array != null) {
              if (array.size() > 0) {
                  if (key.equals("u")) {
                      return;
                  }
              }
          } else {
              array = new ArrayList<String>();
              this._attributes.put(key, array);
          }
          // Add the String to the array list
          array.add(value);
      }