code: public void setThumbnailSize(final Dimension thumbnailSize) {
  		Dimension currSize = getThumbnailSize();
  
  		if (thumbnailSize != null) {
  			if (thumbnailSize.height == 0 || thumbnailSize.width == 0) {
  				throw new IllegalArgumentException(
  						"Thumbnail size cannot have a height or width of zero.");
  			}
  			if (thumbnailSize.height == -1 && thumbnailSize.width == -1) {
  				throw new IllegalArgumentException(
  						"Thumbnail size cannot have both height and width set to -1.");
  			}
  		}
  		if (!Objects.equals(thumbnailSize, currSize)) {
  			getOrCreateComponentModel().thumbnailSize = thumbnailSize;
  		}
  	}
docs: Set the thumbnail size. Null uses the default size.
  <p>
  To scale thumbnails to a certain height or width, use -1 on the scalable dimension. For example, to scale
  thumbnails to 64 pixels high but maintain the correct width ration, set Height to 64 and Width to -1.
  </p>
  
  @param thumbnailSize the thumbnail size or null for default