@Override
        public void onError(Throwable cause) {
            requireNonNull(cause, "cause");

            if (closed) {
                return;
            }

            closed = true;
            final StreamWriter<StreamMessage<HttpData>> emitter = MultipartEncoder.this.emitter;
            assert emitter != null;
            emitter.abort(cause);
        }
Reactive processor that encodes a stream of {@link BodyPart}s into an HTTP payload.
core/src/main/java/com/linecorp/armeria/common/multipart/MultipartEncoder.java