Revert default_missing_value to default_value

[Hoverbear]

Description

We don't need to do this anymore. It was some change I was testing that didn't work, and I forgot to remove it.

Checklist

• Formatted with cargo fmt
• Built with nix build
• Ran flake checks with nix flake check
• Added or updated relevant tests (leave unchecked if not applicable)
• Added or updated relevant documentation (leave unchecked if not applicable)
• Linked to related issues (leave unchecked if not applicable)

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