Fixed #37116 -- Explained why a code is useful with a ValidationError.

[jacobtylerwalls]

Trac ticket number

ticket-37116

Branch description

Flesh out why a code is useful here.

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Checklist

• This PR follows the contribution guidelines.
• This PR does not disclose a security vulnerability (see vulnerability reporting).
• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period (see guidelines).
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• I have checked the "Has patch" ticket flag in the Trac system.
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[jacobtylerwalls]

Thanks @arthru, merged in 9551424!