Fixes #16 : Handle null values gracefully

[GurtejSohi]

Description

Fixes #16

Serialization of NULL_VALUE (Value.newBuilder().setNullValue(NullValue.NULL_VALUE).build()) yields the string - "null", which when deserialized was previously returning the Value as null. Although, we handle null also using the isNull() method (which is why it wasn't affecting the client), we also log an error saying that it is unexpected because ideally, we shouldn't be working with null - instead we should be using the null placeholder - NULL_VALUE.

So, this change tells the JsonDeserializer to use the null placeholder (NULL_VALUE) on encountering the string - "null", which ensures that we never get null config on deserialization.

Testing

Added unit test

Checklist:

• My changes generate no new warnings
• I have added tests that prove my fix is effective
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Merging #34 (8395426) into main (620171f) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main      #34      +/-   ##
============================================
+ Coverage     90.50%   90.52%   +0.02%     
  Complexity      109      109              
============================================
  Files            14       14              
  Lines           400      401       +1     
  Branches         18       18              
============================================
+ Hits            362      363       +1     
  Misses           32       32              
  Partials          6        6              

Flag	Coverage Δ	Complexity Δ
integration	90.52% <100.00%> (+0.02%)	0.00 <0.00> (ø)
unit	88.41% <100.00%> (+0.03%)	0.00 <0.00> (ø)

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Impacted Files	Coverage Δ	Complexity Δ
...ypertrace/config/service/store/ConfigDocument.java	89.47% <100.00%> (+0.28%)	13.00 <0.00> (ø)

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[GurtejSohi]

This assertion fails without the above changes in ConfigDocument as in that case, the config document - ConfigDocument.fromJson(configDocument.toJson()) would have config value as null.

[github-actions]

Unit Test Results

10 files  ±0  10 suites  ±0   4s ⏱️ -2s
32 tests +1  32 ✔️ +1  0 💤 ±0  0 ❌ ±0 

Results for commit 527ceb4. ± Comparison against base commit 620171f.