- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [ ] I have checked the [FAQ](https://github.com/apache/dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.6-SNAPSHOT
* Operating System version: Mac
* Java version: 1.8

### Steps to reproduce this issue

run dubbo-samples-stub sample

### Expected Result

"stub - greeting dubbo"

### Actual Result

return "greeting dubbo"

}
    @Override
    public <T> T getProxy(Invoker<T> invoker, boolean generic) throws RpcException {
        return proxyFactory.getProxy(invoker, generic);
    }
    @Override
    @SuppressWarnings({"unchecked", "rawtypes"})
    public <T> T getProxy(Invoker<T> invoker) throws RpcException {
        T proxy = proxyFactory.getProxy(invoker);
        if (GenericService.class != invoker.getInterface()) {
            URL url = invoker.getUrl();
            String stub = url.getParameter(STUB_KEY, url.getParameter(LOCAL_KEY));
            if (ConfigUtils.isNotEmpty(stub)) {
                Class<?> serviceType = invoker.getInterface();
                if (ConfigUtils.isDefault(stub)) {
                    if (url.hasParameter(STUB_KEY)) {
                        stub = serviceType.getName() + "Stub";
                    } else {
                        stub = serviceType.getName() + "Local";
                    }
                }
                try {
                    Class<?> stubClass = ReflectUtils.forName(stub);
                    if (!serviceType.isAssignableFrom(stubClass)) {
                        throw new IllegalStateException("The stub implementation class " + stubClass.getName() + " not implement interface " + serviceType.getName());
                    }
                    try {
                        Constructor<?> constructor = ReflectUtils.findConstructor(stubClass, serviceType);
                        proxy = (T) constructor.newInstance(new Object[]{proxy});