MC-30156: [Magento Cloud] - Indexer Error happens after appled a patch

- Fix return value of Magento\PageBuilder\Model\Stage\Preview::isPreviewMode() must be of the type boolean, null returned

Author: bubasuma

app/code/Magento/PageBuilder/Model/Stage/Preview.php

@@ -42,6 +42,11 @@ class Preview
      */
     private $scopeConfig;
 
+    /**
+     * @var bool
+     */
+    private $isPreview = false;
+
     /**
      * Preview constructor.
      * @param \Magento\Store\Model\App\Emulation $emulation
@@ -67,11 +72,6 @@ public function __construct(
         $this->scopeConfig = $scopeConfig;
     }
 
-    /**
-     * @var bool
-     */
-    private $isPreview;
-
     /**
      * Retrieve the area in which the preview needs to be ran in
      *