From cd8011633934496f5021660bb09ce6bd8f5d612a Mon Sep 17 00:00:00 2001
From: Thea Flowers <thea@winterbloom.com>
Date: Thu, 9 May 2024 10:27:04 -0400
Subject: [PATCH] Fix crash when mkdocs_theme.yml is empty

Fixes #3699
---
 mkdocs/tests/theme_tests.py | 19 +++++++++++++++++++
 mkdocs/theme.py             |  3 +++
 2 files changed, 22 insertions(+)

diff --git a/mkdocs/tests/theme_tests.py b/mkdocs/tests/theme_tests.py
index f9989fb3..ddc526bf 100644
--- a/mkdocs/tests/theme_tests.py
+++ b/mkdocs/tests/theme_tests.py
@@ -104,3 +104,22 @@ class ThemeTests(unittest.TestCase):
                 ],
             )
             self.assertEqual(theme.static_templates, {'sitemap.xml', 'child.html', 'parent.html'})
+
+    def test_empty_config_file(self):
+        # Test for themes with *empty* mkdocs_theme.yml.
+        # See https://github.com/mkdocs/mkdocs/issues/3699
+        m = mock.Mock(
+            # yaml.load returns "None" for an empty file
+            side_effect=[None]
+        )
+        with mock.patch('yaml.load', m) as m:
+            theme = Theme(name='mkdocs')
+            # Should only have the default name and locale __vars set in
+            # Theme.__init__()
+            self.assertEqual(
+                dict(theme),
+                {
+                    'name': 'mkdocs',
+                    'locale': parse_locale('en'),
+                },
+            )
diff --git a/mkdocs/theme.py b/mkdocs/theme.py
index bf587201..b45f1079 100644
--- a/mkdocs/theme.py
+++ b/mkdocs/theme.py
@@ -138,6 +138,9 @@ class Theme(MutableMapping[str, Any]):
                 f"Please upgrade to a current version of the theme."
             )
 
+        if theme_config is None:
+            theme_config = {}
+
         log.debug(f"Loaded theme configuration for '{name}' from '{file_path}': {theme_config}")
 
         if parent_theme := theme_config.pop('extends', None):