def mutate_json_record(self, json_record):
for attr_name in json_record:<EOL><INDENT>attr = json_record[attr_name]<EOL>if isinstance(attr, datetime):<EOL><INDENT>json_record[attr_name] = attr.isoformat()<EOL><DEDENT><DEDENT>
Override it to convert fields of `json_record` to needed types.

        Default implementation converts `datetime` to string in ISO8601 format.