JavaFX - 更改页面时HTMLElements为null

Question

当用户点击链接时，我想更改页面，然后加载相关信息。

但是，HTMLElement始终为null。

以下是代码：

WebViewPanel.java

//to be used in JFX Thread
public void loadURLFX(final String url) {
    if (Misc.stringHasContent(url)) {

        String tmp = toURL(url);

        if (tmp == null) {
            tmp = toURL("http://" + url);
        }

        boolean invalidURL = false;
        InputStream stream = null;
        try {
            URL urlObj = new URL(tmp);
            stream = urlObj.openStream();
        } catch (Exception e) {
            invalidURL = true;
        } finally {
            try {
                stream.close();
            } catch (Exception ex) {
            }
            stream = null;
        }

        if (!invalidURL) {
            engine.load(tmp);
        } else {
            //https://www.google.com.sg/search?q=searchTerm
            engine.load("https://www.google.com.sg/search?q=" + url);
        }
    }
}

App.java

public void load(){
    if(Platform.isFxApplicationThread()){
        webViewPanel.loadURLFX(App.class.getResource("/hello.html").toExternalForm());
        HTMLElement element = (HTMLElement) WebMisc.getHTMLElement(webViewPanel.getWebEngine(), "menu");
    }
}

element始终为空。我该怎么做才能解决它？