Allow setting nulls to data attributes

[longquanzheng]

for #164

[codecov]

Codecov Report

Merging #166 (2a7bc8e) into main (6243726) will increase coverage by 0.21%.
The diff coverage is 0.00%.

❗ Current head 2a7bc8e differs from pull request most recent head ba99106. Consider uploading reports for the commit ba99106 to get more accurate results

@@             Coverage Diff              @@
##               main     #166      +/-   ##
============================================
+ Coverage     68.23%   68.45%   +0.21%     
- Complexity      322      325       +3     
============================================
  Files            55       55              
  Lines          1379     1379              
  Branches        129      129              
============================================
+ Hits            941      944       +3     
+ Misses          364      363       -1     
+ Partials         74       72       -2     

Impacted Files	Coverage Δ
...orkflow/core/persistence/DataAttributesRWImpl.java	65.62% <0.00%> (+6.25%)	⬆️

... and 1 file with indirect coverage changes

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