fix: keep null in severity filter list

[MichaelMraka]

HMS-10653

Description

Associated Jira ticket: # (issue)

Please include a summary of the change, what this fixes/creates/improves.

How to test the PR

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Before the change

After the change

Dependent work link

Checklist:

• The commit message has the Jira ticket linked
• PR has a short description
• Screenshots before and after the change are added
• Tests for the changes have been added
• README.md is updated if necessary
• Needs additional dependent work

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.29%. Comparing base (a40e6cc) to head (343c88b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1699      +/-   ##
==========================================
+ Coverage   77.27%   77.29%   +0.02%     
==========================================
  Files         103      103              
  Lines        3287     3290       +3     
  Branches      735      744       +9     
==========================================
+ Hits         2540     2543       +3     
  Misses        668      668              
  Partials       79       79              

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[TenSt]

lgtm!

[swadeley]

/retest