adding support for 'when' modelled after changes to fqm-execution in fqm-execution/pull/273

[gregory-akins]

This PR includes:

• Coverage results for case...when...then
• Coverage results for null literal
• coverage results for false literal
• e.g.

Pull requests into cqm-execution require the following. Submitter and reviewer should :white_check_mark: when done. For items that are not-applicable, note it's not-applicable ("N/A") and :white_check_mark:.

Came out of ONC Jira ticket: https://oncprojectracking.healthit.gov/support/browse/BONNIEMAT-1696

Submitter:

• [X] This pull request describes why these changes were made.
• [ ] Internal ticket for this PR:
• [ ] Internal ticket links to this PR
• [X] Code diff has been done and been reviewed
• [X] Tests are included and test edge cases
• [X] Tests have been run locally and pass

Reviewer 1:

Name:

• [ ] Code is maintainable and reusable, reuses existing code and infrastructure where appropriate, and accomplishes the task’s purpose
• [ ] The tests appropriately test the new code, including edge cases
• [ ] You have tried to break the code

Reviewer 2:

Name:

• [ ] Code is maintainable and reusable, reuses existing code and infrastructure where appropriate, and accomplishes the task’s purpose
• [ ] The tests appropriately test the new code, including edge cases
• [ ] You have tried to break the code

[adongare]

I don't think null literal is working correctly.

Update- this is fixed now