From 0dec22f72f360d1d6c728e8d567ec0a175876fed 2014-11-01 23:41:08
From: MinRK <benjaminrk@gmail.com>
Date: 2014-11-01 23:41:08
Subject: [PATCH] convert v3->v4: only set collapsed metadata if value is defined

---

diff --git a/IPython/nbformat/v4/convert.py b/IPython/nbformat/v4/convert.py
index 6770d80..a73f2e6 100644
--- a/IPython/nbformat/v4/convert.py
+++ b/IPython/nbformat/v4/convert.py
@@ -83,7 +83,8 @@ def upgrade_cell(cell):
     cell.setdefault('metadata', NotebookNode())
     if cell.cell_type == 'code':
         cell.pop('language', '')
-        cell.metadata.collapsed = cell.pop('collapsed')
+        if 'collapsed' in cell:
+            cell.metadata['collapsed'] = cell.pop('collapsed')
         cell.source = cell.pop('input', '')
         cell.execution_count = cell.pop('prompt_number', None)
         cell.outputs = upgrade_outputs(cell.outputs)