fix: selectors: adds null value check to checkbox group onchange

[dkilgore-eightfold]

SUMMARY:

• Compares for value in CheckBoxGroup onChange
• Adds some typing

JIRA TASK (Eightfold Employees Only):

ENG-39406

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• [] Tests for this change already exist
• I have added unittests for this change

TEST PLAN:

Pull the pr branch and run yarn and yarn storybook. Verify the CheckBoxGroup story behaves as expected.

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[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@80f9c6f). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #497   +/-   ##
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  Coverage        ?   84.87%           
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  Files           ?      784           
  Lines           ?    16297           
  Branches        ?     5622           
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  Hits            ?    13832           
  Misses          ?     2397           
  Partials        ?       68           

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