When I set `path` in ServiceConfig or `contextpath` in ProtocolConfig, RestProtocol throws NPE on this line:
https://github.com/apache/incubator-dubbo/blob/master/dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/RestProtocol.java#L93
```java
Class implClass = ApplicationModel.getProviderModel(url.getServiceKey()).getServiceInstance().getClass();
```

<dubbo:service path="test" interface="org.apache.dubbo.samples.rest.api.facade.UserRestService" ref="userRestService"
                   protocol="rest" validation="true"/>

This is because we use `group/interface:version` as the key when putting ProviderModel:
```java
Application.initProviderModel(group/interface:version, providerModel)
```
but use `group/path:version` to get, as showed above.

I think to unify to `path` would solve this problem.

}
    }
    
    public String[] getParamsToRegistry(String[] defaultKeys, String[] additionalParameterKeys) {
        int additionalLen = additionalParameterKeys.length;
        String[] registryParams = new String[defaultKeys.length + additionalLen];
        System.arraycopy(defaultKeys, 0, registryParams, 0, defaultKeys.length);
        System.arraycopy(additionalParameterKeys, 0, registryParams, defaultKeys.length, additionalLen);
        return registryParams;
    }
    @Override
    public void destroy() {
        List<Exporter<?>> exporters = new ArrayList<Exporter<?>>(bounds.values());
        for (Exporter<?> exporter : exporters) {
            exporter.unexport();
        }
        bounds.clear();
        DynamicConfiguration.getDynamicConfiguration()
                .removeListener(ApplicationModel.getApplication() + CONFIGURATORS_SUFFIX, providerConfigurationListener);
    }
    
    private static URL getConfigedInvokerUrl(List<Configurator> configurators, URL url) {
        if (configurators != null && configurators.size() > 0) {
            for (Configurator configurator : configurators) {
                url = configurator.configure(url);
            }
        }
        return url;
    }
    public static class InvokerDelegate<T> extends InvokerWrapper<T> {