bugfix:map.toString error

[kongwang]

Ⅰ. Describe what this PR did

StringUtils.toString() method output error when instance of map

Ⅱ. Does this pull request fix one issue?

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

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[slievrly]

LGTM

[Haiyoung]

approved this pull request.

[sharajava]

okey to me

[codecov-io]

Codecov Report

Merging #1409 into develop will decrease coverage by 0.09%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##             develop   #1409     +/-   ##
===========================================
- Coverage       45.5%   45.4%   -0.1%     
+ Complexity      1661    1660      -1     
===========================================
  Files            345     345             
  Lines          12665   12666      +1     
  Branches        1598    1571     -27     
===========================================
- Hits            5763    5751     -12     
+ Misses          6251    6250      -1     
- Partials         651     665     +14

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/io/seata/common/util/StringUtils.java	26.25% <0%> (-0.34%)	15 <0> (ø)
...obuf/convertor/BranchRegisterRequestConvertor.java	88% <0%> (-8%)	3% <0%> (ø)
...buf/convertor/GlobalLockQueryRequestConvertor.java	92.59% <0%> (-7.41%)	3% <0%> (ø)
...obuf/convertor/GlobalRollbackRequestConvertor.java	94.73% <0%> (-5.27%)	3% <0%> (ø)
...otobuf/convertor/GlobalStatusRequestConvertor.java	94.73% <0%> (-5.27%)	3% <0%> (ø)
...otobuf/convertor/GlobalCommitRequestConvertor.java	94.73% <0%> (-5.27%)	3% <0%> (ø)
...protobuf/convertor/RegisterTMRequestConvertor.java	95.45% <0%> (-4.55%)	3% <0%> (ø)
...protobuf/convertor/RegisterRMRequestConvertor.java	91.66% <0%> (-4.17%)	3% <0%> (ø)
...otobuf/convertor/BranchReportRequestConvertor.java	92.59% <0%> (-3.71%)	3% <0%> (ø)
...otobuf/convertor/BranchCommitRequestConvertor.java	96.42% <0%> (-3.58%)	3% <0%> (ø)
... and 6 more

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