DataMapper ORM v1.8.0

[eluser]WanWizard[/eluser]
Datamapper fetches language strings in the following situations:
- error message for a failed validation rules (for custom validation rules, see http://datamapper.wanwizard.eu/pages/val...r.Messages)
- for transation messages ( are defined in datamapper's language file )
- for errors related to saving relations ( are defined in datamapper's language file )
- for fieldname localisations ( needs {model}_{field} entries in the language file )

Unique is a method you have defined somewhere, and is therefore a custom validation rule. If it fails, it will produce an error and will fetch the message. Not sure why the key in the log would be empty.