[BUG-FIX] Wrap set of missing values in a tuple before passing it to pw.apply_with_type

[Bilpapster]

Description

Fixes #21

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Testing

• I have tested this change locally
• I have added tests that prove my fix is effective or that my feature works
• All new and existing tests pass

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[Gatmatz]

Great job identifying and fixing the bug. This looks good to me — we can go ahead and merge.

[Bilpapster]

Thanks George! Just enabled auto-merge at the repository level, so, hopefully we can have PRs that are accepted to be merged automatically from now on.