fix: check for null value during form validation

[Jshhhh]

Issue #, if available:

Description of changes:

• Null values in forms caused non required fields to be validated
• Add check for null value during validation function

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[codecov-commenter]

Codecov Report

Merging #902 (8387195) into main (166f92b) will decrease coverage by 0.17%.
The diff coverage is 58.33%.

@@            Coverage Diff             @@
##             main     #902      +/-   ##
==========================================
- Coverage   93.06%   92.89%   -0.17%     
==========================================
  Files         117      118       +1     
  Lines        5047     5068      +21     
  Branches     1485     1489       +4     
==========================================
+ Hits         4697     4708      +11     
- Misses        329      339      +10     
  Partials       21       21              

Impacted Files	Coverage Δ
...gen-ui-react/lib/utils/forms/validation-helpers.ts	56.25% <56.25%> (ø)
...ges/codegen-ui-react/lib/utils/forms/validation.ts	95.00% <62.50%> (-2.90%)	⬇️

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