public static synchronized void registerProvider(ZuulBlockFallbackProvider provider) {
        AssertUtil.notNull(provider, "fallback provider cannot be null");
        String route = provider.getRoute();
        if ("*".equals(route) || route == null) {
            defaultFallbackProvider = provider;
        } else {
            fallbackProviderCache.put(route, provider);
        }
    }
@Test
    public void testRegisterProvider() throws Exception {
        MyNullResponseFallBackProvider myNullResponseFallBackProvider = new MyNullResponseFallBackProvider();
        ZuulBlockFallbackManager.registerProvider(myNullResponseFallBackProvider);
        Assert.assertEquals(myNullResponseFallBackProvider.getRoute(), ROUTE);
        Assert.assertNull(myNullResponseFallBackProvider.fallbackResponse(ROUTE, new FlowException("flow ex")));
    }