fix #873 init default value for import config

[github-ygy]

Ⅰ. Describe what this PR did

init default value for import config

Ⅱ. Does this pull request fix one issue?

fix #873

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #874 into develop will increase coverage by 0.01%.
The diff coverage is 66.66%.

@@              Coverage Diff              @@
##             develop     #874      +/-   ##
=============================================
+ Coverage      38.65%   38.66%   +0.01%     
  Complexity      1026     1026              
=============================================
  Files            220      220              
  Lines           8507     8507              
  Branches        1028     1028              
=============================================
+ Hits            3288     3289       +1     
+ Misses          4828     4826       -2     
- Partials         391      392       +1

Impacted Files	Coverage Δ	Complexity Δ
.../java/io/seata/core/rpc/netty/NettyBaseConfig.java	22.22% <66.66%> (ø)	2 <0> (ø)	⬇️
...eata/core/rpc/netty/AbstractRpcRemotingClient.java	17.7% <0%> (+0.47%)	7% <0%> (ø)	⬇️

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[slievrly]

LGTM

[xingfudeshi]

LGTM