make `NavigationService` throw-helpers `protected` (instead of `private`)

[Palatis]

Pull request type

Please check the type of change your PR introduces:

• [x] Update
• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes

What is the current behavior?

NavigationService has their throw-helpers declared with private modifier, which made derived classes difficult.

Issue Number: N/A

What is the new behavior?

• Make them protected so they can be used in derived classes.

Other information