HtmlUnit driver doesn't execute JavaScript
Your class HtmlUnitDriver is not part of the standard Selenium package, is it? As far as i know, for HtmlUnit you have to create a RemoteWebDriver instance with either DesiredCapabilities.HtmlUnit() or DesiredCapabilities.HtmlUnitWithJavaScript().
Can you loook inside your HtmlUnitDriver class? Maybe DesiredCapabilities.HtmlUnit() instead of DesiredCapabilities.HtmlUnitWithJavaScript() is used!?