Fix NPE when invoke asynchronously use JDKProxy.

[ujjboy]

Fix #75

[codecov-io]

Codecov Report

Merging #77 into 5.3 will increase coverage by 0.05%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                5.3      #77      +/-   ##
============================================
+ Coverage     63.44%   63.49%   +0.05%     
- Complexity      583      584       +1     
============================================
  Files           263      263              
  Lines         11226    11228       +2     
  Branches       1871     1872       +1     
============================================
+ Hits           7122     7129       +7     
  Misses         3136     3136              
+ Partials        968      963       -5

Impacted Files	Coverage Δ	Complexity Δ
...lipay/sofa/rpc/proxy/jdk/JDKInvocationHandler.java	80.76% <100%> (+1.6%)	0 <0> (ø)	⬇️
.../com/alipay/sofa/rpc/log/MiddlewareLoggerImpl.java	76.81% <0%> (-5.8%)	0% <0%> (ø)
.../alipay/sofa/rpc/registry/local/LocalRegistry.java	57.83% <0%> (+0.6%)	26% <0%> (+1%)	⬆️
...ava/com/alipay/sofa/rpc/config/RegistryConfig.java	36% <0%> (+1%)	0% <0%> (ø)	⬇️
.../java/com/alipay/sofa/rpc/log/SLF4JLoggerImpl.java	100% <0%> (+1.51%)	0% <0%> (ø)	⬇️
...n/java/com/alipay/sofa/rpc/common/SofaConfigs.java	85.71% <0%> (+1.78%)	0% <0%> (ø)	⬇️
...lipay/sofa/rpc/proxy/javassist/JavassistProxy.java	79.06% <0%> (+3.87%)	0% <0%> (ø)	⬇️

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