code: private void notifyOnRestoredDefaultValue(@NonNull final Preference preference,
                                                final Object oldValue, final Object newValue) {
          for (RestoreDefaultsListener listener : restoreDefaultsListeners) {
              listener.onRestoredDefaultValue(this, preference, oldValue,
                      newValue != null ? newValue : oldValue);
          }
      }
docs: Notifies all registered listeners, that the default value of a specific preference has been
  be restored.
  
  @param preference
  The preference, whose default value has been restored, as an instance of the class
  {@link Preference}. The preference may not be null
  @param oldValue
  The old value of the preference, whose default value has been restored, as an
  instance of the class {@link Object}
  @param newValue
  The new value of the preference, whose default value has been restored, as an
  instance of the class {@link Object}