Adding a rule to a pam field

Hi, we want to change the web sync to look at the web.description field, rather than item.description so that we can enter more characters.
Please could you tell me the correct code to put in the field mappings so that it will show the web.description when there is something in the field, but if blank it will show the item.description.

thanks,
Naomi

hi, i have figured it out no worries
thanks