Raise serializable exception when encountering invalid workflow connection

                        if "output_name" not in conn_dict or "id" not in conn_dict:

                            template = "Invalid connection [%s] - must be dict with output_name and id fields."

                            message = template % conn_dict

                            raise exceptions.MessageException(message)

                            raise exceptions.MalformedContents(message)

                        external_id = conn_dict["id"]

                        if external_id not in steps_by_external_id:

                            raise KeyError(f"Failed to find external id {external_id} in {steps_by_external_id.keys()}")

                            raise exceptions.MalformedContents(

                                f"Invalid connection. Failed to find input step id {external_id}"

                            )

                        output_step = steps_by_external_id[external_id]

                        output_name = conn_dict["output_name"]