use null check instead of as

packages/app/src/server/models/page.ts

@@ -608,7 +608,10 @@ schema.statics.getParentAndFillAncestors = async function(path: string, user): P
   await this.bulkWrite(operations);
 
   const parentId = ancestorsMap.get(parentPath)._id; // get parent page id to fetch updated parent parent
-  const createdParent = await this.findOne({ _id: parentId }) as PageDocument;
+  const createdParent = await this.findOne({ _id: parentId });
+  if (createdParent == null) {
+    throw Error('updated parent not Found');
+  }
   return createdParent;
 };