code: public PresenceSubscriber addBuddy(String uri, int duration, long timeout) {
      return addBuddy(uri, duration, null, timeout);
    }
docs: This method is the same as addBuddy(uri, duration, eventId, timeout) except that no event "id"
  parameter will be included.
  
  @param uri the URI (ie, sip:bob@nist.gov) of the buddy to be added to the list.
  @param duration the duration in seconds to put in the SUBSCRIBE message. If 0, this is
  equivalent to a fetch except that the buddy stays in the buddy list even though the
  subscription won't be active.
  @param timeout The maximum amount of time to wait for a SUBSCRIBE response, in milliseconds.
  Use a value of 0 to wait indefinitely.
  @return PresenceSubscriber object representing the buddy if the operation is successful so far,
  null otherwise.