code: public byte[] downloadAttachmentContent(Attachment issueAttachment)
              throws RedmineException {
          final ByteArrayOutputStream baos = new ByteArrayOutputStream();
          downloadAttachmentContent(issueAttachment, baos);
          try {
              baos.close();
          } catch (IOException e) {
              throw new RedmineInternalError();
          }
          return baos.toByteArray();
      }
docs: Downloads the content of an {@link com.taskadapter.redmineapi.bean.Attachment} from the Redmine server.
  
  @param issueAttachment the {@link com.taskadapter.redmineapi.bean.Attachment}
  @return the content of the attachment as a byte[] array
  @throws RedmineCommunicationException thrown in case the download fails