code: private Observable<ConversationComparison> updateLocalConversationList(final ConversationComparison conversationComparison) {
  
          return Observable.zip(persistenceController.deleteConversations(conversationComparison.conversationsToDelete),
                  persistenceController.upsertConversations(conversationComparison.conversationsToAdd),
                  persistenceController.updateConversations(conversationComparison.conversationsToUpdate),
                  (success1, success2, success3) -> success1 && success2 && success3)
                  .map(result -> {
                      conversationComparison.addSuccess(result);
                      return conversationComparison;
                  });
      }
docs: Update list of local conversations.
  
  @param conversationComparison Describes differences in local and remote participant list.
  @return Observable returning unchanged argument to further processing.