Help removing "NaN" from my formula results

Hello,

I am using the formula listed below to depicted the total days a project was active. For projects that do not yet have a date, I receive “NaN Days” in my column, which I would rather it say “0 Days.” How do I replace NaN with 0?

DAYS({Completion Date},{Date Approved}) &" Days"

Try
IF({Completion Date}=“”,“0 Days”, DAYS({Completion Date},{Date Approved}) &" Days")