Issue #3510517: Call to Undefined Method.

Closes #3510517

modules/wsdata_field/wsdata_field.module

@@ -7,10 +7,12 @@
 
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityFormInterface;
 use Drupal\Core\Field\FieldConfigInterface;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Url;
+use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\field_ui\FieldUI;
 use Drupal\wsdata_field\Entity\WSFieldConfig;
 
@@ -124,19 +126,21 @@ function wsdata_field_entity_load(array $entities, $entity_type_id) {
  */
 function wsdata_field_form_alter(&$form, FormStateInterface $form_state, $form_id) {
   if ('node_delete_multiple_confirm_form' !== $form_id && (preg_match('/^node_(.*)_edit_form/', $form_id) || preg_match('/^node_(.*)_form/', $form_id))) {
-    $entity = $form_state->getFormObject()->getEntity();
-    if ($entity->getEntityTypeId() == 'node') {
-      $fields = $entity->getFieldDefinitions();
-      foreach ($fields as $field) {
-        // Get the fields storage definitions.
-        $field_storage = $field->getFieldStorageDefinition();
-        // Check if it has the custom storage flag set to true.
-        if ($field_storage->hasCustomStorage()) {
-          // Check to make sure the object is of type FieldStorageConfig.
-          if (is_a($field_storage, 'Drupal\field\Entity\FieldStorageConfig')) {
+    $form_object = $form_state->getFormObject();
+    // Ensure the form object has a getEntity method before calling it.
+    if ($form_object instanceof EntityFormInterface) {
+      $entity = $form_object->getEntity();
+      if ($entity instanceof ContentEntityInterface) {
+        $fields = $entity->getFieldDefinitions();
+        foreach ($fields as $field) {
+          // Get the fields storage definitions.
+          $field_storage = $field->getFieldStorageDefinition();
+          // Check if custom storage flag set to true and
+          // the field storage object has correct class.
+          if ($field_storage->hasCustomStorage() && $field_storage instanceof FieldStorageConfig) {
             // Fetch the wsfield config entity.
             $wsfield_config = \Drupal::service('entity_type.manager')->getStorage('wsfield_config')->load($field_storage->get('field_name'));
-            if ($wsfield_config != NULL) {
+            if ($wsfield_config !== NULL) {
               // Make the field hidden by adding a class.
               $form[$field_storage->get('field_name')]['#attributes']['class'][] = 'hidden';
             }