Non-null assertion cleanup PART 1

[growabeard]

Contributor checklist

• This pull request is on a separate branch and not the main branch
• I have tested my code with the ./gradlew lintKotlin detekt test command as directed in the testing section of the contributing guide

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Description

This PR is fixing non-null assertions in a few classes, with tests accompanying the changes.

This is only the first PR in a series of work.

Related issue

• Clean up non-null assertions in the codebase #705

[andrewtavis]

Thanks for the PR, @growabeard! Would you be able to fix the Ktlint issues?

[growabeard]

Egg on my face. I ran lintKotlin but ignored the output.. 👻

[andrewtavis]

No stress, @growabeard! @prince-0408 and/or @Roniscend: Would either of you be able to do an initial review?

How many parts do you think you'll do for the PRs, @growabeard? Just wondering if you have an impression :)

[growabeard]

@andrewtavis

How many parts do you think you'll do for the PRs, @growabeard? Just wondering if you have an impression :)

I think just one more actually. I should have the second one ready this week.

[andrewtavis]

Sounds great, @growabeard!