IPTC/EXIF Mapping, Default Values

Hi David. Mapping iptc field 2#0120 caption into the WordPress field caption is not an issue, but what to do if this iptc field is empty. In this case I want to put the content of the field title into the field caption. How to do this? I know the conditional thing and within the markup item I can get this to work, but for the iptc mapping I can’t make it.

Something like this :
Caption = if iptc:0#120 not empty then iptc:0#120 else iptc:0#005

Thank you in advance