Minor

semf1.py

@@ -226,11 +226,11 @@ def _validate_input_format(
         raise ValueError(f"Predictions and references must have the same length. "
                          f"Got {len(predictions)} predictions and {len(references)} references.")
 
-    def is_list_of_strings_at_depth(lst_obj, depth: int):
-        return is_nested_list_of_type(lst_obj, element_type=str, depth=depth)
+    if len(predictions) == 0:
+        raise ValueError("Can't have empty inputs")
 
     def check_format(lst_obj, expected_depth: int, name: str):
-        is_valid, error_message = is_list_of_strings_at_depth(lst_obj, expected_depth)
+        is_valid, error_message = is_nested_list_of_type(lst_obj, element_type=str, depth=expected_depth)
         if not is_valid:
             raise ValueError(f"{name} are not in the expected format.\n"
                              f"Error: {error_message}.")