Add null protection

[asbjornu]

Add null guards to GitObject and ObjectId to avoid NullReferenceException.

Description

This PR is an exploration of which null guards we can add to avoid NullReferenceException and possibly also avoiding null before they reach GitVersion.Core.

Related Issue

Resolves #2775.

The following issues aren't fixed as this PR doesn't address the underlying issues, but this PR will provide a much more informative stack trace so if anyone encounters the underlying issues again, we'll have a better chance at figuring out what the issue is and actually fix it.

Closes #2605.
Closes #2631.
Closes #2695.
Closes #2734.
Closes #2825.

Motivation and Context

See #2775 and all linked issues.

How Has This Been Tested?

I'm counting on our existing test coverage to sufficiently exercise the code involved.

Screenshots (if appropriate):

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[arturcic]

Can you also add the null check for these classes? BranchCollection, Reference, TagCollection

[arturcic]

LGTM

[arturcic]

@asbjornu will you also add for the other 2?

[asbjornu]

@arturcic, yes, that's the plan. I just want every commit to be green so I'm confident that none of the added null checks break anything – and if they do, I want to know which one it is. But I'm unable to get a successful build out of 2790f27 due to some docker login failing. Ideas?

[asbjornu]

It's rather peculiar that the ❌ on the commit is red with lots of tests failing:

…while the summary is all green ✅ :

[arturcic]

https://github.com/GitTools/GitVersion/actions/runs/2088880949 - this one seems to be green

[asbjornu]

Yea, I just want this ❌ green. 😅

I'll amend and force push, hopefully it turns green then.

[arturcic]

I think it's failing on your branch on your repo, not on GtiTools, because it's trying to use some envvars that you do not have setup

[asbjornu]

Yes, that was my thought as well, @arturcic. But that doesn't explain why previous commits as well as the amended commit are all green? 🤔

Anyway, as the commit is now successful, I'll continue pushing the other files as well.

[mergify]

Thank you @asbjornu for your contribution!