fixed a bug where None was converted to JSON null instead of DB null

shared/selene/data/skill/repository/setting.py

@@ -47,11 +47,17 @@ class SkillSettingRepository(RepositoryBase):
             new_skill_settings: AccountSkillSetting,
             skill_ids: List[str]
     ):
+        if new_skill_settings.settings_values is None:
+            serialized_settings_values = None
+        else:
+            serialized_settings_values = json.dumps(
+                new_skill_settings.settings_values
+            )
         db_request = self._build_db_request(
             'update_device_skill_settings.sql',
             args=dict(
                 account_id=account_id,
-                settings_values=json.dumps(new_skill_settings.settings_values),
+                settings_values=serialized_settings_values,
                 skill_id=tuple(skill_ids),
                 device_names=tuple(new_skill_settings.device_names)
             )