[#noissue] Replace StringUtils.defaultString with Objects.toString for null handling

[emeroad]

…r null handling

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 13 lines in your changes missing coverage. Please review.

Project coverage is 33.59%. Comparing base (cbdb41f) to head (0dfd1a7).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...t/inspector/web/definition/metric/field/Field.java	0.00%	4 Missing ⚠️
...pinpoint/web/vo/tree/ApplicationAgentHostList.java	0.00%	3 Missing ⚠️
...int/inspector/web/definition/MetricDefinition.java	0.00%	2 Missing ⚠️
...or/applicationmap/dao/hbase/HbaseMapInLinkDao.java	0.00%	1 Missing ⚠️
...r/applicationmap/dao/hbase/HbaseMapOutLinkDao.java	0.00%	1 Missing ⚠️
...nt/web/applicationmap/dao/mapper/InLinkMapper.java	0.00%	1 Missing ⚠️
...eb/vo/activethread/AgentActiveThreadCountList.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #12488      +/-   ##
============================================
- Coverage     33.59%   33.59%   -0.01%     
+ Complexity    10739    10738       -1     
============================================
  Files          3941     3941              
  Lines         91809    91809              
  Branches       9553     9553              
============================================
- Hits          30846    30841       -5     
- Misses        58328    58332       +4     
- Partials       2635     2636       +1     

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