fix: prevent filtering by linked_character_id: None when character_id is None in generation queries.

repos/generation_repo.py

@@ -29,8 +29,6 @@ class GenerationRepo:
         args = {}
         if character_id is not None:
             args["linked_character_id"] = character_id
-        else:
-            args["linked_character_id"] = None
         if status is not None:
             args["status"] = status
         res = await self.collection.find(args).sort("created_at", -1).skip(