public static Class<?> getAssistInterface(Object proxyBean)
        throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException,
        NoSuchMethodException, InvocationTargetException {
        if (proxyBean == null) {
            return null;
        }
        if (!isDubboProxyName(proxyBean.getClass().getName())) {
            return null;
        }
        Field handlerField = proxyBean.getClass().getDeclaredField("handler");
        handlerField.setAccessible(true);
        Object invokerInvocationHandler = handlerField.get(proxyBean);
        Field invokerField = invokerInvocationHandler.getClass().getDeclaredField("invoker");
        invokerField.setAccessible(true);
        Object invoker = invokerField.get(invokerInvocationHandler);
        Field failoverClusterInvokerField = invoker.getClass().getDeclaredField("invoker");
        failoverClusterInvokerField.setAccessible(true);
        Object failoverClusterInvoker = failoverClusterInvokerField.get(invoker);
        return (Class<?>)ReflectionUtil.invokeMethod(failoverClusterInvoker,
            "getInterface");
    }
@Test
    public void testGetAssistInterfaceForNull() throws NoSuchFieldException, InvocationTargetException, IllegalAccessException, NoSuchMethodException {
        assertNull(DubboUtil.getAssistInterface(null));
    }