code: public function add($cookie)
      {
          if ($this->readOnly) {
              throw new InvalidCallException('The cookie collection is read only.');
          }
          $this->_cookies[$cookie->name] = $cookie;
      }
docs: Adds a cookie to the collection.
  If there is already a cookie with the same name in the collection, it will be removed first.
  @param Cookie $cookie the cookie to be added
  @throws InvalidCallException if the cookie collection is read only