NVL on a CONCAT expression in a Cross tab report

Content

Hi,

Please see screenshot below.

Where it says "no value", I am using the following:

nvl(concat(tasks.status_id, ' / ' , tasks.pct_complete),'-')

However, it's still outputting "No Value". What am I doing wrong? If there is not an associated task for that incident, I want to display a hyphen