docs: protected final String[] addAttribute(String key, String value) {
          this._toString = null;
          ArrayList<String> array = this._attributes.get(key);
          String[] old_array = null;
          if (array != null) {
              if (array.size() > 0) {
                  old_array = new String[array.size()];
                  old_array = array.toArray(old_array);
                  if (key.equals("u")) {
                      /**
                       * Do not set multiple values for accessID
                       **/
                      return old_array;
                  }
              }
          } else {
              array = new ArrayList<String>();
              this._attributes.put(key, array);
          }
          // Add the String to the array list
          array.add(value);
          return old_array;
      }