set createdAt null or Date type

packages/app/src/client/services/ContextExtractor.tsx

@@ -14,7 +14,6 @@ import {
 const { isTrashPage: _isTrashPage } = pagePathUtils;
 
 const jsonNull = 'null';
-const dateNull = 'null';
 
 const ContextExtractorOnce: FC = () => {
 
@@ -32,7 +31,16 @@ const ContextExtractorOnce: FC = () => {
   const path = decodeURI(mainContent?.getAttribute('data-path') || '');
   const pageId = mainContent?.getAttribute('data-page-id') || null;
   const revisionCreatedAt = +(mainContent?.getAttribute('data-page-revision-created') || '');
-  const createdAt = new Date(mainContent?.getAttribute('data-page-created-at') || dateNull);
+
+  let createdAt: Date | null;
+  const createdAtAttribute = mainContent?.getAttribute('data-page-created-at');
+  if (createdAtAttribute != null) {
+    createdAt = new Date(createdAtAttribute);
+  }
+  else {
+    createdAt = null;
+  }
+
   const updatedAt = mainContent?.getAttribute('data-page-updated-at');
   const deletedAt = mainContent?.getAttribute('data-page-deleted-at') || null;
   const isUserPage = JSON.parse(mainContent?.getAttribute('data-page-user') || jsonNull);