Avoid handling JSON_ARRAY as multi value JSON during transformation

[shounakmk219]

The transform pipeline is failing with an ArrayIndexOutOfBoundsException when it encounters a JSON column value with empty json array as JSON value is not standardised (empty array -> null) https://github.com/apache/pinot/blob/master/pinot-segment-local/src/main/java/org/apache/pinot/segment/local/recordtransformer/DataTypeTransformer.java#L97

Earlier empty array for json datatype was getting extracted as string, now its getting extracted as Object[] due to the change at https://github.com/apache/pinot/pull/14547/files#diff-7ac5349f9d75e27a62a063dbf81db3ed30c8de052b4ffa7719187e4babaa60baR66
which leads to isMultiValue returning true for empty json array

convertMultiValue returns Object[] while convertSingleValue returns a string
https://github.com/apache/pinot/blob/master/pinot-spi/src/main/java/org/apache/pinot/spi/data/readers/BaseRecordExtractor.java#L39

  public Object convert(Object value) {
    Object convertedValue;
    if (isMultiValue(value)) {
      convertedValue = convertMultiValue(value);
    } else if (isMap(value)) {
      convertedValue = convertMap(value);
    } else if (isRecord(value)) {
      convertedValue = convertRecord(value);
    } else {
      convertedValue = convertSingleValue(value);
    }
    return convertedValue;
  }

Updating the transform logic to handle the empty array for JSON datatype

[xiangfu0]

Please fix the tests.

[shounakmk219]

OK, looks like I got few things wrong about the extractor, fixing it.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 63.90%. Comparing base (59551e4) to head (5bed8c2).
Report is 1525 commits behind head on master.

Files with missing lines	Patch %	Lines
...t/local/recordtransformer/DataTypeTransformer.java	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #14738      +/-   ##
============================================
+ Coverage     61.75%   63.90%   +2.15%     
- Complexity      207     1607    +1400     
============================================
  Files          2436     2703     +267     
  Lines        133233   150731   +17498     
  Branches      20636    23290    +2654     
============================================
+ Hits          82274    96329   +14055     
- Misses        44911    47183    +2272     
- Partials       6048     7219    +1171     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (+99.99%)	⬆️
integration	100.00% <ø> (+99.99%)	⬆️
integration1	100.00% <ø> (+99.99%)	⬆️
integration2	0.00% <ø> (ø)
java-11	63.80% <33.33%> (+2.09%)	⬆️
java-21	63.78% <33.33%> (+2.15%)	⬆️
skip-bytebuffers-false	63.83% <33.33%> (+2.08%)	⬆️
skip-bytebuffers-true	63.75% <33.33%> (+36.02%)	⬆️
temurin	63.90% <33.33%> (+2.15%)	⬆️
unittests	63.90% <33.33%> (+2.15%)	⬆️
unittests1	56.27% <33.33%> (+9.38%)	⬆️
unittests2	34.24% <33.33%> (+6.51%)	⬆️

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