- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] 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: 2.7.3-SNAPSHOT
* Operating System version: macOs
* Java version: JDK 1.8

### Steps to reproduce this issue

1. We cannot getFuture from alibaba RpcContext after setFuture, the result is null.
```
CompletableFuture future = new CompletableFuture();
com.alibaba.dubbo.rpc.RpcContext.getContext().setFuture(future);
Future result = com.alibaba.dubbo.rpc.RpcContext.getContext().getFuture();
```

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result
result should be same new FutureAdapter(future);

### Actual Result

result is null.

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

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 * this work for additional information regarding copyright ownership.
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 * (the "License"); you may not use this file except in compliance with
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package com.alibaba.dubbo.rpc;
import org.apache.dubbo.rpc.FutureContext;
import com.alibaba.dubbo.rpc.protocol.dubbo.FutureAdapter;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Future;
@Deprecated
public class RpcContext extends org.apache.dubbo.rpc.RpcContext {
    public static RpcContext getContext() {
        return newInstance(org.apache.dubbo.rpc.RpcContext.getContext());
    }