Avoid nullable `schemaPath` and `instancePath`

[jonasfj]

Ultimate problem:

schemaPath and instancePath on ValidationError is never null, so users shouldn't need to check for null.

How it was fixed:

schemaPath and instancePath was made non-nullable.

Testing suggestions:

N/A.

Potential areas of regression:

nits:

• Users who access schemaPath or instancePath may get a warning, if they were doing null checks (most probably where). This warning is likely harmless and easy to fix by removing the unnecessary null check.
• Users who made a class that implements ValidationError may rely on instancePath and schemaPath being nullable. However:
  • It's unlikely that implementing ValidationError is common (the constructor is private, so it was probably not intended for subclassing).
  • ValidationError should probably be a made a final class ValidationError.

[aviary-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure
• Verify aviary.yaml coverage of security relevant code

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Questions or Comments? Reach out on Slack: #support-infosec.

[michaelcarter-wf]

@Workiva/release-management-p