Remove SomePersistField

[halogenandtoast]

Issue

SomePersistField exists only to convert to PersistValue. Furthermore, we end up with a type-class instance with unexpected behavior due to how fromPersistValue works.

Solution

We can replace SomePersistValue with PersistValue directly.

After submitting your PR:

N.B.

Yesod book's description for the generated code should be updated as well.

TODO For Author

• Update the Changelog.md file with a link to your PR
• Bumped the version number if there isn't an (unreleased) on the Changelog
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)