code: private StyleableStringProperty imageUrlProperty() {
  
          if (imageUrl == null) {
              imageUrl = CssHelper.createStyleableStringProperty(this, PROP_NAME_IMAGE_URL, GRAPHIC, () -> {
                  final String url = imageUrlProperty().get();
  
                  if (url != null) {
                      final Image img = StyleManager.getInstance().getCachedImage(url);
  
                      if (img != null) {
                          graphicProperty().set(new ImageView(img));
                      }
                  } else {
                      graphicProperty().set(null);
                  }
              });
          }
          return imageUrl;
      }
docs: ---------------------- IMAGE URL