docs: @SuppressWarnings("WeakerAccess")
      @UiThread
      public boolean popToRoot(@Nullable ControllerChangeHandler changeHandler) {
          ThreadUtils.ensureMainThread();
  
          if (backstack.size() > 1) {
              //noinspection ConstantConditions
              popToTransaction(backstack.root(), changeHandler);
              return true;
          } else {
              return false;
          }
      }