SQL fails when dxcc is null

[sipsmi]

https://github.com/magicbug/Cloudlog/blob/c874ec994c280ac35bde7989ee6f166c3b1caa2b/application/models/Logbook_model.php#L4337

This has been discussed, sometimes when typing in a callsign when login a QSO the lookup fails and the log shows an error since the call to get_entity can be null for unworked callsigns.

I work around this with if ( ! isset($dxcc) || empty($dxcc)) { return '' ; }

as the first line in the get_entity function.

It seems a safe thing to do - can it be added?

Thanks