@Test
public void testNull() {

    invocation.setMethodName("echo1");
    invocation.setParameterTypes(new Class<?>[]{String.class});
    invocation.setArguments(new Object[]{"arg3"});
    cacheFilter.invoke(invoker4, invocation);
    RpcResult rpcResult1 = (RpcResult) cacheFilter.invoke(invoker1, invocation);
    RpcResult rpcResult2 = (RpcResult) cacheFilter.invoke(invoker2, invocation);
    Assert.assertEquals(rpcResult1.getValue(), "value1");
    Assert.assertEquals(rpcResult2.getValue(), "value1");
}