Handle missing attachment key

Author: Jimmie Goode

jupyter_ydoc/ydoc.py

@@ -90,7 +90,7 @@ def get_cell(self, index: int) -> Dict[str, Any]:
         if "id" in cell and meta["nbformat"] == 4 and meta["nbformat_minor"] <= 4:
             # strip cell IDs if we have notebook format 4.0-4.4
             del cell["id"]
-        if cell["cell_type"] in ["raw", "markdown"] and not cell["attachments"]:
+        if "attachments" in cell and cell["cell_type"] in ["raw", "markdown"] and not cell["attachments"]:
             del cell["attachments"]
         return cell
 
@@ -137,7 +137,7 @@ def get(self):
             if "id" in cell and meta["nbformat"] == 4 and meta["nbformat_minor"] <= 4:
                 # strip cell IDs if we have notebook format 4.0-4.4
                 del cell["id"]
-            if cell["cell_type"] in ["raw", "markdown"] and not cell["attachments"]:
+            if "attachments" in cell and cell["cell_type"] in ["raw", "markdown"] and not cell["attachments"]:
                 del cell["attachments"]
             cells.append(cell)