[EP-tech] How to allow users to search for NULL values?

[Jan Ploski]

Hi,

(How) can I let the users search for eprints that have NULL in a 
particular field?

For example, I see there are options "No Preference", "Yes" and "No" 
available for a boolean field, but I'd like people to be able to find 
eprints with "No Value" - to make data quality control easier. Same 
would make sense for other field types, too - is there some standard 
option somewhere?

Regards,
Jan Ploski