fix: update settlePlan field type to support null values

[gryumov]

Pull request checklist

• Did you bump the project version?
• Did you add a description to the Pull Request?
• Did you add new tests?
• Did you add reviewers?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.29%. Comparing base (33b11d8) to head (5c07002).

Additional details and impacted files

@@          Coverage Diff           @@
##           master     #64   +/-   ##
======================================
  Coverage    2.29%   2.29%           
======================================
  Files         183     183           
  Lines        2262    2262           
======================================
  Hits           52      52           
  Misses       2210    2210           

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