[boardgames] Remove expansion_ids key if not needed

vrobbler/apps/scrobbles/scrobblers.py

@@ -413,6 +413,8 @@ def email_scrobble_board_game(
             expansion.expansion_for_boardgame = base_game
             expansion.save()
             log_data["expansion_ids"].append(expansion.id)
+        if log_data.get("expansion_ids") == []:
+            log_data.pop("expansion_ids")
 
         if play_dict.get("locationRefId", False):
             log_data["location_id"] = locations[