Use constant null place holder

[Jackie-Jiang]

This PR also fixes some wrong type casting for BYTES type

[codecov-commenter]

Codecov Report

Merging #11615 (65249b0) into master (fef4e64) will decrease coverage by 0.03%.
Report is 2 commits behind head on master.
The diff coverage is 57.74%.

@@             Coverage Diff              @@
##             master   #11615      +/-   ##
============================================
- Coverage     63.07%   63.04%   -0.03%     
  Complexity     1146     1146              
============================================
  Files          2326     2326              
  Lines        124884   124891       +7     
  Branches      19141    19141              
============================================
- Hits          78767    78740      -27     
- Misses        40504    40540      +36     
+ Partials       5613     5611       -2     

Flag	Coverage Δ
integration	<0.01% <0.00%> (ø)
integration1	<0.01% <0.00%> (ø)
integration2	0.00% <0.00%> (ø)
java-11	50.03% <57.74%> (-12.99%)	⬇️
java-17	62.90% <57.74%> (-0.01%)	⬇️
java-20	62.90% <57.74%> (-0.03%)	⬇️
temurin	63.04% <57.74%> (-0.03%)	⬇️
unittests	63.04% <57.74%> (-0.03%)	⬇️
unittests1	67.27% <57.74%> (-0.02%)	⬇️
unittests2	14.48% <0.00%> (-0.02%)	⬇️

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Files Changed	Coverage Δ
...e/pinot/common/function/scalar/ArrayFunctions.java	86.84% <0.00%> (ø)
.../transform/function/CoalesceTransformFunction.java	62.23% <16.66%> (ø)
...ator/transform/function/CaseTransformFunction.java	57.32% <35.71%> (ø)
...sform/function/ScalarTransformFunctionWrapper.java	81.20% <37.50%> (ø)
...ator/transform/function/BaseTransformFunction.java	71.39% <53.84%> (ø)
...java/org/apache/pinot/common/utils/DataSchema.java	61.95% <100.00%> (ø)
...va/org/apache/pinot/spi/utils/CommonConstants.java	28.00% <100.00%> (+7.56%)	⬆️

... and 9 files with indirect coverage changes

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