code: private void cleanMixedAttributes() {
          currentFieldAttributes.remove(HttpHeaderValues.CHARSET);
          currentFieldAttributes.remove(HttpHeaderNames.CONTENT_LENGTH);
          currentFieldAttributes.remove(HttpHeaderNames.CONTENT_TRANSFER_ENCODING);
          currentFieldAttributes.remove(HttpHeaderNames.CONTENT_TYPE);
          currentFieldAttributes.remove(HttpHeaderValues.FILENAME);
      }
docs: Remove all Attributes that should be cleaned between two FileUpload in
  Mixed mode