Reproduce and fix #1070

docs/CHANGELOG.md

@@ -1,12 +1,19 @@
 Jupytext ChangeLog
 ==================
 
+1.14.7-dev (2023-06-??)
+-------------------
+
+**Fixed**
+- Fix opening of notebooks with empty YAML header ([#1070](https://github.com/mwouts/jupytext/issues/1070))
+
+
 1.14.6 (2023-06-04)
 -------------------
 
 **Changed**
 - This version comes with a build requirement `jupyterlab>=3,<4`, as the Jupyterlab
-extension for Jupytext is not compatible with JupyterLab 4 yet (#1054)
+extension for Jupytext is not compatible with JupyterLab 4 yet ([#1054](https://github.com/mwouts/jupytext/issues/1054))
 - The JupyterLab extension was released to `npm` in version 1.3.9.
 
 1.14.5 (2023-02-25)

jupytext/formats.py

@@ -280,6 +280,8 @@ def read_metadata(text, ext):
     # MyST has the metadata at the root level
     if not metadata and ext in myst_extensions() and text.startswith("---"):
         for header in yaml.safe_load_all(text):
+            if not isinstance(header, dict):
+                continue
             if (
                 header.get("jupytext", {})
                 .get("text_representation", {})

tests/test_read_simple_markdown.py

@@ -941,3 +941,18 @@ def test_hide_notebook_metadata(
     compare(md2, md)
     nb2 = jupytext.reads(md, "md")
     compare_notebooks(nb2, nb)
+
+
+def test_notebook_with_empty_header_1070(
+    md="""---
+
+---
+
+This file has empty frontmatter.
+""",
+):
+    nb = jupytext.reads(md, fmt="md:markdown")
+    md2 = jupytext.writes(nb, "md")
+    compare(md2, md)
+    nb2 = jupytext.reads(md, "md")
+    compare_notebooks(nb2, nb)