Enable case <expr> when syntax

[ChrisJar]

Ex: case a when 0 then NULL which is equivalent to case when a=0 then NULL

[codecov-commenter]

Codecov Report

Merging #1148 (99b815f) into main (7888493) will increase coverage by 0.11%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##             main    #1148      +/-   ##
==========================================
+ Coverage   81.30%   81.42%   +0.11%     
==========================================
  Files          78       78              
  Lines        4414     4414              
  Branches      799      799              
==========================================
+ Hits         3589     3594       +5     
+ Misses        649      640       -9     
- Partials      176      180       +4     

see 1 file with indirect coverage changes

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[ayushdg]

cc: @jdye64

[jdye64]

Logic makes sense to me. Thanks for adding this @ChrisJar. Is there an issue for this? I ask because I likely will need to implement this in Arrow DataFusion Python later as well or this logic might accidentally be removed.

[jdye64]

FYI - Made PR to mimic this behavior in Arrow DataFusion Python apache/datafusion-python#388