/**
  * {@inheritdoc}
  */
 public function submitConfigurationForm(array &$form, FormStateInterface $form_state)
 {
     $facet_source_id = $this->facet->getFacetSourceId();
     $field_identifier = $form_state->getValue('facet_source_configs')[$facet_source_id]['field_identifier'];
     $this->facet->setFieldIdentifier($field_identifier);
 }