Do not remove None values in RepoCardData serialization

src/huggingface_hub/repocard_data.py

@@ -185,7 +185,7 @@ def to_dict(self):
 
         data_dict = copy.deepcopy(self.__dict__)
         self._to_dict(data_dict)
-        return _remove_none(data_dict)
+        return {key: value for key, value in data_dict.items() if value is not None}
 
     def _to_dict(self, data_dict):
         """Use this method in child classes to alter the dict representation of the data. Alter the dict in-place.

tests/test_repocard_data.py

@@ -237,6 +237,19 @@ def test_model_card_unique_tags(self):
         data = ModelCardData(tags=["tag2", "tag1", "tag2", "tag3"])
         assert data.tags == ["tag2", "tag1", "tag3"]
 
+    def test_remove_top_level_none_values(self):
+        as_obj = ModelCardData(tags=["tag1", None], foo={"bar": 3, "baz": None}, pipeline_tag=None)
+        as_dict = as_obj.to_dict()
+
+        assert as_obj.tags == ["tag1", None]
+        assert as_dict["tags"] == ["tag1", None]  # none value inside list should be kept
+
+        assert as_obj.foo == {"bar": 3, "baz": None}
+        assert as_dict["foo"] == {"bar": 3, "baz": None}  # none value inside dict should be kept
+
+        assert as_obj.pipeline_tag is None
+        assert "pipeline_tag" not in as_dict  # top level none value should be removed
+
 
 class DatasetCardDataTest(unittest.TestCase):
     def test_train_eval_index_keys_updated(self):