code: public synchronized void onContactsChanged(boolean isEmpty) {
          if (isContactsEmpty.get() != isEmpty) {
              context.getPreferences().putBool("app.contacts.empty", isEmpty);
              isContactsEmpty.change(isEmpty);
          }
          if (!isEmpty) {
              if (isAppEmpty.get()) {
                  context.getPreferences().putBool("app.empty", false);
                  isAppEmpty.change(false);
              }
          }
      }
docs: Notify from Modules about contacts state changed
  
  @param isEmpty is contacts empty