[#12019] Add logic to prevent error when metadata is missing.

[minwoo-jung]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.

Project coverage is 33.97%. Comparing base (4f6700a) to head (c11f3a8).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...com/navercorp/pinpoint/otlp/web/vo/MetricData.java	0.00%	5 Missing ⚠️
...int/otlp/web/service/OtlpMetricWebServiceImpl.java	0.00%	3 Missing ⚠️
...vercorp/pinpoint/otlp/web/view/MetricDataView.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #12020      +/-   ##
============================================
- Coverage     33.98%   33.97%   -0.02%     
+ Complexity    10471    10469       -2     
============================================
  Files          3727     3727              
  Lines         88849    88858       +9     
  Branches       9457     9458       +1     
============================================
- Hits          30195    30188       -7     
- Misses        56052    56070      +18     
+ Partials       2602     2600       -2     

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