I am running a Unbound as upstream DNS and is has also it’s own lists that could return Null (0.0.0.0). Those are seen by Pi-hole as perfectly fine IP addresses that have the button “blacklist” available.
You can whitelist them but will not change anything because the IP still will be 0.0.0.0
So the request is to omit the button when the resolved IP is Null and comes from upstream.
The message could be “Blocked, 0.0.0.0 address”