JsDialogHandler crash on Prompt dialog and callback continue

gistfile1.cs

public class JsDialogHandler : IJsDialogHandler
{
  string result = "default";
  public bool OnJSDialog(IWebBrowser browserControl, IBrowser browser, string originUrl,
            CefJsDialogType dialogType, string messageText, string defaultPromptText,
            IJsDialogCallback callback, ref bool suppressMessage)
  {
    suppressMessage = true;
    if (dialogType == CefJsDialogType.Prompt)
    {
      parent.Invoke(new Action(() =>
      {
          result = ShowTextInputForm(); // Show a form and get text input
      }));
      if(null != callback && !callback.IsDisposed)
      {
          callback.Continue(true, result);
      }
    }
    else
    {
       MessageBox.Show(messageText, "Status", MessageBoxButtons.OKCancel, MessageBoxIcon.Asterisk);
    }
    return true;
  }
  // Rest of class