--- /dev/null
+<?php
+
+namespace Drupal\Core\Entity\Plugin\EntityReferenceSelection;
+
+use Drupal\Core\Database\Query\SelectInterface;
+use Drupal\Core\Entity\EntityReferenceSelection\SelectionInterface;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Defines a fallback plugin for missing entity_reference selection plugins.
+ *
+ * @EntityReferenceSelection(
+ * id = "broken",
+ * label = @Translation("Broken/Missing")
+ * )
+ */
+class Broken implements SelectionInterface {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+ $form['selection_handler'] = [
+ '#markup' => t('The selected selection handler is broken.'),
+ ];
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function validateConfigurationForm(array &$form, FormStateInterface $form_state) { }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function submitConfigurationForm(array &$form, FormStateInterface $form_state) { }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
+ return [];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function countReferenceableEntities($match = NULL, $match_operator = 'CONTAINS') {
+ return 0;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function validateReferenceableEntities(array $ids) {
+ return [];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function entityQueryAlter(SelectInterface $query) { }
+
+}