fix(batch): Correctly handle child_exceptions being None

aws_lambda_powertools/utilities/batch/exceptions.py

@@ -16,7 +16,7 @@ def __init__(self, msg="", child_exceptions: Optional[List[ExceptionInfo]] = Non
 
     def format_exceptions(self, parent_exception_str):
         exception_list = [f"{parent_exception_str}\n"]
-        for exception in self.child_exceptions:
+        for exception in self.child_exceptions or []:
             extype, ex, tb = exception
             formatted = "".join(traceback.format_exception(extype, ex, tb))
             exception_list.append(formatted)

tests/functional/test_utilities_batch.py

@@ -908,3 +908,7 @@ def lambda_handler(event, context):
 
     # THEN raise BatchProcessingError
     assert "All records failed processing. " in str(e.value)
+
+
+def test_child_exceptions_is_none():
+    assert str(SQSBatchProcessingError()) == "\n"