/**
* {@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);
}