Cleanup stuff reported by PHPStan

Closes #3512191

modules/form_decorator_example/src/FormDecorator/NodeCreatedDate.php

@@ -6,15 +6,16 @@ namespace Drupal\form_decorator_example\FormDecorator;
 
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\form_decorator\FormDecoratorBase;
 use Drupal\form_decorator\Attribute\FormDecorator;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\form_decorator\ContentEntityFormDecoratorBase;
+use Drupal\node\NodeInterface;
 
 /**
  * Adds a created date picker to the node form.
  */
 #[FormDecorator('form_node_form_alter')]
-final class NodeCreatedDate extends FormDecoratorBase {
+final class NodeCreatedDate extends ContentEntityFormDecoratorBase {
 
   use StringTranslationTrait;
 
@@ -23,9 +24,11 @@ final class NodeCreatedDate extends FormDecoratorBase {
    */
   public function buildForm(array $form, FormStateInterface $form_state, ...$args) {
     $form = $this->inner->buildForm($form, $form_state, ...$args);
+    $node = $this->getEntity();
+    assert($node instanceof NodeInterface);
     $created_time = time();
     if (!$this->getEntity()->isNew()) {
-      $created_time = $this->getEntity()->getCreatedTime();
+      $created_time = $node->getCreatedTime();
     }
 
     $form['created_datepicker'] = [
@@ -40,8 +43,10 @@ final class NodeCreatedDate extends FormDecoratorBase {
   /**
    * {@inheritdoc}
    */
-  public function save(array &$form, FormStateInterface $form_state) {
-    $this->getEntity()->setCreatedTime($form_state->getValue('created_datepicker')->getTimestamp());
+  public function save(array $form, FormStateInterface $form_state) {
+    $node = $this->getEntity();
+    assert($node instanceof NodeInterface);
+    $node->setCreatedTime($form_state->getValue('created_datepicker')->getTimestamp());
     return $this->inner->save($form, $form_state);
   }