Method WriteOptional

library/cpp/json/json_writer.h:149–153

        template <typename T>
        void WriteOptional(const TStringBuf& key, const TMaybe<T>& value) {
            if (value) {
                Write(key, *value);
            }
        }

        void WriteOptional(const TStringBuf&, const TNothing&) {
            // nothing to do