fix(eslint-plugin): [no-unnecessary-type-assertion] allow non-null assertion for void type

[yeonjuan]

PR Checklist

• Addresses an existing open issue: fixes Bug: [@typescript-eslint/no-unnecessary-type-assertion] False positives when using non-null assertion operator for functions with potentially void return type #8906
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

[typescript-eslint]

Thanks for the PR, @yeonjuan!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[auvred]

Looks great! 🔥

[kirkwaiblinger]

question - should void just be part of isNullableType?

[yeonjuan]

@kirkwaiblinger A quick check shows that modifying isNullableType seems to work fine. However, if we do modify this function, it would be nice to add some tests to other rules that use it. What do you think about creating a separate issue?

[kirkwaiblinger]

Agreed!

[JoshuaKGoldberg]

Nice!