message: Also check for truthy classname before adding class
diff: @@ -47,5 +47,5 @@ export function removeClass(node: HTMLElement, className: string): void {
  export function addClass(node: HTMLElement, className: string): void {
  const cl = node.classList
  - if (!cl.contains(className)) cl.add(className)
  + if (className && !cl.contains(className)) cl.add(className)
  }
  