fix(aci): set action config values to null instead of '' or undefined

[ameliahsu]

The Action validators were failing because the Action configs expect null for nonexistent values, not ''.

Additionally, when stripping Actions of their targetDisplay, we were previously removing the field from the config, but to keep typing consistent we should be setting targetDisplay: null

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #104796      +/-   ##
===========================================
- Coverage   80.48%    80.48%   -0.01%     
===========================================
  Files        9359      9359              
  Lines      401722    401720       -2     
  Branches    25822     25821       -1     
===========================================
- Hits       323326    323324       -2     
  Misses      77954     77954              
  Partials      442       442