fix: Fix error if timestamp is None

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = yt-dlp-FixupMtime
-version = 1.1.0
+version = 1.1.1
 
 [options]
 packages = find_namespace:

test/test_fixup_mtime.py

@@ -33,6 +33,12 @@ def setUp(self):
     def tearDown(self):
         shutil.rmtree(self.temp_dir)
 
+    def test__striptime_or_none_with_none_timestamp(self):
+        timestamp = None
+        format_code = self.pp._mtime_format
+        expected = None
+        self.assertEqual(self.pp._strptime_or_none(timestamp, format_code), expected)
+
     def test__strptime_or_none_with_invalid_timestamp(self):
         timestamp = 'foobar'
         format_code = self.pp._mtime_format

yt_dlp_plugins/postprocessor/fixup_mtime.py

@@ -19,7 +19,9 @@ def __init__(self, downloader=None, mtime_key: str = 'mtime', mtime_format: str
         self._mtime_key = mtime_key
         self._mtime_format = re.sub(r'%%', '%', mtime_format)
 
-    def _strptime_or_none(self, timestamp: Union[float, int, str], format_code: str) -> Optional[datetime.datetime]:
+    def _strptime_or_none(self, timestamp: Union[float, int, str, None], format_code: str) -> Optional[datetime.datetime]:
+        if timestamp is None:
+            return None
         if isinstance(timestamp, (float, int)):
             return datetime.datetime.fromtimestamp(timestamp, datetime.timezone.utc)
         for code in [format_code] + date_formats(day_first=True):