Fix embedding padding_free (#6100)

Co-authored-by: tastelikefeet <[email protected]>

Author: tastelikefeet

swift/llm/template/base.py

@@ -553,7 +553,7 @@ def packing_row(self, row: List[Dict[str, Any]]) -> Dict[str, Any]:
             length.append(r['length'])
         for key in keys:
             if key in {'input_ids', 'labels', 'loss_scale'}:
-                packed[key] = sum((x[key] for x in row), start=[])
+                packed[key] = sum((x.get(key) or [] for x in row), start=[])
             elif key == 'length':
                 packed[key] = sum((x[key] for x in row))
             elif key == 'channel':