code: function(el, val) {
                          if (val == null || val === "") {
                              el.removeAttribute("src");
                              return null;
                          } else {
                              el.setAttribute("src", val);
                              return val;
                          }
                      }
docs: For the `src` attribute we are using a setter function to prevent values such as an empty string or null from being set. An `img` tag attempts to fetch the `src` when it is set, so we need to prevent that from happening by removing the attribute instead.