code: @Override
      public Calendar reply(Calendar request) {
          Calendar reply = transform(Method.REPLY, request);
          reply.validate();
          return reply;
      }
docs: <pre>
  3.3.3.  REPLY
  
  The "REPLY" method in a "VFREEBUSY" calendar component is used to
  respond to a busy time request.  The method is sent by the recipient
  of a busy time request to the originator of the request.
  
  The "REPLY" method may also be used to respond to an unsuccessful
  "REQUEST" method.  Depending on the "REQUEST-STATUS" value, no busy
  time information may be returned.
  </pre>