Issue #3200856: Fix Reference and none isset checker error

src/EventSubscriber/LayoutBuilderIdsConfigureSection.php

@@ -50,7 +50,7 @@ class LayoutBuilderIdsConfigureSection implements EventSubscriberInterface {
       // Once this issue gets fixed in core then we can use the
       // proper validate procedures.  Until then we need to add the
       // form id without the random value.
-      $form_state = &$event->getFormState();
+      $form_state = $event->getFormState();
       $form['#id'] = Html::getId($form_state->getBuildInfo()['form_id']);
 
       // Get the config for the section.
@@ -61,7 +61,7 @@ class LayoutBuilderIdsConfigureSection implements EventSubscriberInterface {
         '#type' => 'textfield',
         '#title' => 'Section ID',
         '#weight' => 99,
-        '#default_value' => $config['layout_builder_id'] ?: NULL,
+        '#default_value' => $config['layout_builder_id'] ?? NULL,
         '#description' => t('Section ID is an optional setting which is used to support an anchor link to this block. For example, entering "feature" lets you link directly to this section by adding "#feature" to the end of the URL.</br>IDs should start with a letter, may only contain letters, numbers, underscores, hyphens, and periods, and should be unique on the page.'),
       ];