Port zero closed but not stealth

Can anyone shed light on this, its from a scan at GRC on my own computer, everything is stealth except port zero ?
Further reading says that "Port Zero" does not officially exist. It is defined as an invalid port number. But valid Internet packets can be formed and sent "over the wire" to and from "port 0" just as with any other ports. Is there any way to stealth this port rather than just close it, if not, what risk does this pose (if any.)

Port 0 may not have a standard use but it does exist. My 0 is stealth by the same test.

A closed port is perfectly safe. So, you are good to go

Alphalutra1