@Override
  protected void writeInternal(
      MultipartFile[] byteArrayMultipartFiles, HttpOutputMessage outputMessage) {
    throw new UnsupportedOperationException(
        getClass().getSimpleName() + " does not support writing to HTTP body.");
  }
Construct an {@code AbstractHttpMessageConverter} that can read mulitpart/form-data.

@param bufSize The size of the buffer (in bytes) to read the HTTP multipart body.
form-spring/src/main/java/feign/form/spring/converter/SpringManyMultipartFilesReader.java