com.alibaba cluster、Directory兼容失败

• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.7.4.1
• Operating System version: mac
• Java version: 8

Steps to reproduce this issue

1、Cluster

@Deprecated
public interface Cluster extends org.apache.dubbo.rpc.cluster.Cluster {

    <T> com.alibaba.dubbo.rpc.Invoker<T> join(com.alibaba.dubbo.rpc.cluster.Directory<T> directory) throws
            com.alibaba.dubbo.rpc.RpcException;

    @Override
    default <T> Invoker<T> join(Directory<T> directory) throws RpcException {
        return null;
    }
}

join为什么返回NULL

2、Directory

public interface Directory<T> extends org.apache.dubbo.rpc.cluster.Directory<T> {

    @Override
    URL getUrl();

    List<com.alibaba.dubbo.rpc.Invoker<T>> list(com.alibaba.dubbo.rpc.Invocation invocation) throws com.alibaba.dubbo.rpc.RpcException;

    @Override
    default List<Invoker<T>> list(Invocation invocation) throws RpcException {
        List<com.alibaba.dubbo.rpc.Invoker<T>> res = this.list(new com.alibaba.dubbo.rpc.Invocation.CompatibleInvocation(invocation));
        return res.stream().map(i -> i.getOriginal()).collect(Collectors.toList());
    }
}

缺少兼容Directory，例如CompatibleDirectory

我们有老项目实现了Cluster，如果改新的包，很多项目都要动，量很大，所以需要兼容老的。