diff --git a/sdgx/data_processors/transformers/fixed_combination.py b/sdgx/data_processors/transformers/fixed_combination.py
index e1b919ad..95cba876 100644
--- a/sdgx/data_processors/transformers/fixed_combination.py
+++ b/sdgx/data_processors/transformers/fixed_combination.py
@@ -89,7 +89,7 @@ def fit(self, metadata: Metadata | None = None, **kwargs: dict[str, Any]):
             return
 
         # Check if exist fixed combinations, if not exist, needn't run this auto-detect transform.
-        self.fixed_combinations = metadata.get("fixed_combinations")
+        self.fixed_combinations = metadata.get("fixed_combinations") or dict()
         if not self.is_exist_fixed_combinations:
             logger.info(
                 "Fit data using FixedCombinationTransformer(not existed)... Finished (No action)."