follow up for issue 195

[beiwei30]

What is the purpose of the change

follow up for issue #195

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #3614 into master will increase coverage by 0.05%.
The diff coverage is 68.75%.

@@             Coverage Diff              @@
##             master    #3614      +/-   ##
============================================
+ Coverage     64.14%   64.19%   +0.05%     
  Complexity       71       71              
============================================
  Files           664      665       +1     
  Lines         28653    28844     +191     
  Branches       4769     4787      +18     
============================================
+ Hits          18379    18517     +138     
- Misses         8047     8088      +41     
- Partials       2227     2239      +12

Impacted Files	Coverage Δ	Complexity Δ
...org/apache/dubbo/config/AbstractServiceConfig.java	97.33% <ø> (-0.04%)	0 <0> (ø)
...g/apache/dubbo/config/AbstractReferenceConfig.java	94% <ø> (-0.34%)	0 <0> (ø)
.../org/apache/dubbo/config/spring/ReferenceBean.java	18.62% <0%> (-0.43%)	0 <0> (ø)
...in/java/org/apache/dubbo/config/ServiceConfig.java	54.81% <70%> (+0.8%)	0 <0> (ø)	⬇️
.../java/org/apache/dubbo/config/ReferenceConfig.java	58.21% <71.42%> (+0.49%)	0 <0> (ø)	⬇️
...ubbo/rpc/cluster/support/RegistryAwareCluster.java	0% <0%> (-100%)	0% <0%> (ø)
...c/cluster/support/RegistryAwareClusterInvoker.java	0% <0%> (-25%)	0% <0%> (ø)
...bo/metadata/integration/MetadataReportService.java	78.04% <0%> (-6.17%)	0% <0%> (ø)
...e/dubbo/rpc/cluster/directory/StaticDirectory.java	66.66% <0%> (-5.13%)	0% <0%> (ø)
...c/main/java/org/apache/dubbo/rpc/RpcException.java	82.75% <0%> (-3.45%)	0% <0%> (ø)
... and 28 more

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