Change validations to allow blank but not allow nil

What does this MR do?

• Allow outbound_local_requests_whitelist to be [] but not nil.
• Ensure that code does not crash when outbound_local_requests_whitelist is nil.

Issue: #65096 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers