code: public Observable<ChatResult> handleParticipantsAdded(final String conversationId) {
          return persistenceController.getConversation(conversationId).flatMap(conversation -> {
              if (conversation == null) {
                  return handleNoLocalConversation(conversationId);
              } else {
                  return Observable.fromCallable(() -> new ChatResult(true, null));
              }
          });
      }
docs: Handle participant added to a conversation Foundation SDK event.
  
  @param conversationId Unique conversation id.
  @return Observable with Chat SDK result.