Compile iss

[cvictory]

What is the purpose of the change

fix compile issue.

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a GITHUB_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
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[chickenlj]

LGTM

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@4c01c5e). Click here to learn what that means.
The diff coverage is 66.66%.

@@            Coverage Diff            @@
##             master    #4155   +/-   ##
=========================================
  Coverage          ?   62.29%           
  Complexity        ?      505           
=========================================
  Files             ?      789           
  Lines             ?    34911           
  Branches          ?     5461           
=========================================
  Hits              ?    21749           
  Misses            ?    10653           
  Partials          ?     2509

Impacted Files	Coverage Δ	Complexity Δ
...main/java/org/apache/dubbo/rpc/AsyncRpcResult.java	48.31% <66.66%> (ø)	0 <0> (?)

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