[FYST-1788] Guard against nil values when summing up w2, 1099R state income tax / withheld amounts

[arinchoi03]

Link to pivotal/JIRA issue

• https://codeforamerica.atlassian.net/browse/FYST-1788

Is PM acceptance required? (delete one)

• Yes - don't merge until JIRA issue is accepted!

Reminder: merge main into this branch and get green tests before merging to main

What was done?

• We scoped the guards to the two calculators we saw the errors in and also in the method. We did not implement a guard for 1099G because it is impossible to actually set the value to nil due to the validation for state_income_tax_withheld_amount (numericality)

How to test?

• Describe the testing approach taken to verify the changes, including:

  • Unit/integration/manual tests
  • Test data used: any ID/AZ fixture with W2, edit using w2 edit page state_income_tax_amount by leaving a field blank, you should see an error now instead of being able to proceed (which is what happens in demo)

• Specify any relevant testing environments used: Use heroku

• Risk Assessment

  • no risk

Screenshots (for visual changes)

• Before
• After

[github-actions]

Heroku app: https://gyr-review-app-5635-667d73290da4.herokuapp.com/
View logs: heroku logs --app gyr-review-app-5635 (optionally add --tail)