[pp:mtime] do not overwrite '_mtime' for None values (#5439)

gallery_dl/postprocessor/mtime.py

@@ -33,6 +33,9 @@ class MtimePP(PostProcessor):
 
     def run(self, pathfmt):
         mtime = self._get(pathfmt.kwdict)
+        if mtime is None:
+            return
+
         pathfmt.kwdict["_mtime"] = (
             util.datetime_to_timestamp(mtime)
             if isinstance(mtime, datetime) else

test/test_postprocessor.py

@@ -573,6 +573,16 @@ class MtimeTest(BasePostprocessorTest):
         self._trigger()
         self.assertEqual(self.pathfmt.kwdict["_mtime"], 315532800)
 
+    def test_mtime_none(self):
+        self._create(None, {"date": None})
+        self._trigger()
+        self.assertNotIn("_mtime", self.pathfmt.kwdict)
+
+    def test_mtime_undefined(self):
+        self._create(None, {})
+        self._trigger()
+        self.assertNotIn("_mtime", self.pathfmt.kwdict)
+
     def test_mtime_key(self):
         self._create({"key": "foo"}, {"foo": 315532800})
         self._trigger()