how to show a field in a report if the criteria calls for it

I have a database that keeps track of work orders with all pertinent
information in one table. I have a parameter query set up to search for
certain criteria (status, location and begin and end dates). My report is
set to run off of the query. The criteria for status is setup to allow for
comp, inprg and is null.

Like "*" & [Select a status] & "*" Or Is Null

there is a field for completed date in the query that will only show an
actual date if the work order is either completed or the criteria is left
blank to allow all work orders to show on the report (comp or inprg). I
would like to set it up to only show this completed date field to show on the
report if there is going to be informtion in it. I thought about trying to
use an if statement where it would be true if the status field were either
comp or null and in that case allow the field to show, but if it is still
inprg then the field would not show. I do not know how to tell it to show
the field though. Any help would be greatly appretiated.