fixed some strict mode issues

[marilynel]

#980

Addressed strict mode issues with boolean and null casing in values, and boolean, null, and number as keys.

[sonarqubecloud]

Quality Gate passed

Issues
12 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[stleary]

What problem does this code solve?
Fixes problems where Strict mode was not enforcing case for non-string values, and allowing non-string keys.

Does the code still compile with Java6?
Yes

Risks
Low

Changes to the API?
No

Will this require a new release?
No

Should the documentation be updated?
No

Does it break the unit tests?
No, new unit tests were added

Was any code refactored in this commit?
No. Sonarqube found some minor issues. Submitter can fix them if time permits, otherwise I will fix them later.

Review status
APPROVED

Starting 3-day comment window