handle empty fragment length

update license in JSON

frontend/package.json

@@ -1,6 +1,7 @@
 {
   "name": "vector-admin-frontend",
   "type": "module",
+  "license": "MIT",
   "scripts": {
     "start": "vite --open",
     "build": "vite build",

frontend/src/pages/DocumentView/FragmentList/index.tsx

@@ -232,7 +232,7 @@ const Fragment = ({
           )}
         </td>
         <td className="px-6 py-4">
-          {Object.keys(metadata).length > 0 ? (
+          {Object.keys(metadata)?.length > 0 ? (
             <button
               onClick={() => {
                 document