Issue #2831702 by hatznie, vbouchet, krina.addweb: Fatal error when creating new terms

flat_taxonomy.module

@@ -67,9 +67,12 @@ function flat_taxonomy_taxonomy_term_presave(Term $term) {
   // programmatical save (migration, services, ...).
   $vocabulary = Vocabulary::load($term->getVocabularyId());
 
-  if ($vocabulary->getThirdPartySetting('flat_taxonomy', 'flat') == FLAT_TAXONOMY_FLAT && !empty($term->parent)) {
-    \Drupal::logger('flat_taxonomy')->warning('Illegal parent %parent_tid for the term %name as vocabulary is flat. Parent has been updated.', array('%parent_tid' => $term->parent, '%name' => $term->name));
-    drupal_set_message($this->t('Illegal parent %parent_tid for the term %name as vocabulary is flat. Parent has been updated.', array('%parent_tid' => $term->parent, '%name' => $term->name)), 'warning');
+  if (
+    $vocabulary->getThirdPartySetting('flat_taxonomy', 'flat') == FLAT_TAXONOMY_FLAT
+    && !empty($term->parent->target_id)
+  ) {
+    \Drupal::logger('flat_taxonomy')->warning('Illegal parent %parent_tid for the term %name as vocabulary is flat. Parent has been updated.', array('%parent_tid' => $term->parent->target_id, '%name' => $term->name->value));
+    drupal_set_message(t('Illegal parent %parent_tid for the term %name as vocabulary is flat. Parent has been updated.', array('%parent_tid' => $term->parent->target_id, '%name' => $term->name->value)), 'warning');
 
     // @TODO: Update the term weight so it is ordered after the parent.
     $term->parent = 0;