fix: Failed to execute 'observe' on '_ConnectionObserver': parameter …

…1 is not of type 'Node' or a DOMString.

src/widget.ts

@@ -72,7 +72,7 @@ class ReactWidgetImpl<
  if (this.root === undefined || this.containerElement === undefined) {
  this.containerElement = document.createElement('div');
  this.root = ReactDom.createRoot(this.containerElement);
- this.connectionObserver.observe(this.parentDomNode);
+ this.connectionObserver?.observe?.(this.parentDomNode ?? this.containerElement);
  }
  this.domNodes.push(this.containerElement);
  nextSibling === null ? parent.append(this.containerElement) : nextSibling.before(this.containerElement);