Modernized null checks by using `nameof()` operator

[Lehonti]

Also, decomposed some composite null checks into several, so that the exception would be more specific

Checklist

• [ ] An issue was first created before opening this pull request
• [x] The new code follows the contribution guidelines
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas (Does not apply, it's self-documenting)
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests to ensure that prove my fix is effective or that my feature works (N/A)
• [x] New and existing unit tests pass locally with my changes

[Lehonti]

@aalhour any plans to merge this? It's a quick and easy way to improve the code