Backport PR #158 on branch 0.2.x (Fix metadata issue) (#159)

* backport pr #158

* Fix GitHub CI

---------

Co-authored-by: Frédéric Collonval <fcollonval@users.noreply.github.com>

Author: hbcarlos

.github/workflows/check-release.yml

@@ -15,7 +15,7 @@ jobs:
       matrix:
         group: [check_release, link_check]
         python-version: ["3.9"]
-        node-version: ["14.x"]
+        node-version: ["18.x"]
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/test.yml

@@ -50,7 +50,7 @@ jobs:
 
       - name: Install dependencies
         run: |
-          mamba install python=${{ matrix.python-version }} pip nodejs=16 yarn
+          mamba install python=${{ matrix.python-version }} pip nodejs=18 yarn=1
           pip install .[test]
 
       - name: Build JavaScript assets

jupyter_ydoc/ydoc.py

@@ -163,9 +163,9 @@ def get(self):
 
         return dict(
             cells=cells,
-            metadata=meta["metadata"],
-            nbformat=int(meta["nbformat"]),
-            nbformat_minor=int(meta["nbformat_minor"]),
+            metadata=meta.get("metadata", {}),
+            nbformat=int(meta.get("nbformat", 0)),
+            nbformat_minor=int(meta.get("nbformat_minor", 0)),
         )
 
     def set(self, value):