我收到空指针异常

Question

  public class CJavaScriptExecutor  {
  public static WebDriver driver;
  private static  JavascriptExecutor js= (JavascriptExecutor)driver;
  public  static void highLighElement(WebElement element){

    js.executeScript("arguments[0].setAttribute('style', 'background: 
          yellow; border: 2px solid red;');", element);
}

当我在另一个类中调用Highlight方法的代码如下时，它将引发空指针异常。

    WebElement frame =driver.findElement(By.id("productPillarFrame"));
    CJavaScriptExecutor.highLighElement(frame);