Issue #3490184: All applicable form events should implement RenderEventInterface

modules/content/src/Event/ContentEntityPrepareForm.php

@@ -91,6 +91,9 @@ class ContentEntityPrepareForm extends ContentEntityBaseContentEntity implements
    */
   public function &getRenderArray(): array {
     $form = &$this->getForm();
+    if ($form === NULL) {
+      $form = [];
+    }
     return $form;
   }