Fix PHP notices.

bibcite_footnotes.module

@@ -76,7 +76,7 @@ function bibcite_footnotes_preprocess_bibcite_footnote_list(&$variables) {
 
   $notes['#attached']['library'][] = 'bibcite_footnotes/reference_footnote';
   $dont_show_backlink_text = $config['reference_dont_show_backlink_text'];
-  $sort_references_by = $config['reference_sort_by'];
+
   $citation_tools = new CitationTools();
   if (empty($footnotes)) {
     return;
@@ -241,21 +241,22 @@ function bibcite_footnotes_form_node_form_alter(&$form, FormStateInterface &$for
       /**
        * @var FieldConfig $field_config
        */
-      $field_config = $ief_instance['instance'];
-
-      // Check if this is a bibcite_reference field type.
-      if ($field_config->getSetting('handler') == 'default:bibcite_reference') {
-        $field_name = $field_config->get('field_name');
-        if (!empty($ief_instance['entities'])) {
-
-          foreach ($ief_instance['entities'] as $entity_wrapper) {
-            /**
-             * @var \Drupal\core\Entity\EntityInterface $entity
-             */
-            $entity = $entity_wrapper['entity'];
-            if ($entity->getEntityTypeId() == 'bibcite_reference') {
-              list($citation_text, $citation_key) = bibcite_footnotes_get_ckeditor_select_item($entity);
-              $bibcite_references[] = [$citation_text, $citation_key];
+      if ($field_config = $ief_instance['instance']) {
+
+        // Check if this is a bibcite_reference field type.
+        if ($field_config->getSetting('handler') == 'default:bibcite_reference') {
+          $field_name = $field_config->get('field_name');
+          if (!empty($ief_instance['entities'])) {
+
+            foreach ($ief_instance['entities'] as $entity_wrapper) {
+              /**
+               * @var \Drupal\core\Entity\EntityInterface $entity
+               */
+              $entity = $entity_wrapper['entity'];
+              if ($entity->getEntityTypeId() == 'bibcite_reference') {
+                list($citation_text, $citation_key) = bibcite_footnotes_get_ckeditor_select_item($entity);
+                $bibcite_references[] = [$citation_text, $citation_key];
+              }
             }
           }
         }