code: protected String getFilename(Object part) {
  		if (part instanceof Resource) {
  			Resource resource = (Resource) part;
  			return resource.getFilename();
  		}
  		else {
  			return null;
  		}
  	}
docs: Return the filename of the given multipart part. This value will be used for the
  {@code Content-Disposition} header.
  <p>The default implementation returns {@link Resource#getFilename()} if the part is a
  {@code Resource}, and {@code null} in other cases. Can be overridden in subclasses.
  @param part the part to determine the file name for
  @return the filename, or {@code null} if not known